A STUDY OF THE THERMAL AND PHOTOCHEMICAL REACTIONS

OF GROUP 6 METAL CARBONYL COMPOUNDS

WHEN BOUND TO ORGANIC POLYMER SUPPORTS

Ph.D THESIS

— W —D ublin C ity UNIVERSITY

BYSUPERVISORDATE

GRAHAM RUSSELL BSc. Dr. CONOR LONG AUGUST 1990.

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PeelarationI declare that the work presented in this thesis is based entirely on my research carried out at Dublin City University from October 1987 to August 1990 under the supervision of Dr. Conor Long.

Graham Russell

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CONTENTS PaceTitle page (i)Declaration (ii)Acknowledgements (vii)Abstract (viii)

CHAPTER 1

An Introduction to Polymer-Bound Group 6Metal Carbonyls 1

CHAPTER 2

The Synthesis and Characterisation of Polymer-BoundGroup 6 Metal Carbonyls 31

2.1 Introduction 32

2.2 Preparation of Polymer-Bound Metal Carbonyls 33

2.3 Characterisation of Polvmer-Bound Metal CarbonylSystems 41

2.3.1 Vibrational Spectra of Metal Carbonyls

2.3.2 Infrared Spectroscopic Properties of41

Monomer Complexes 2.3.3 Infrared Spectroscopic Properties of

43

Polymer Complexes 2.3.4 UV/Visible Spectroscopic Properties of

48

Metal Carbonyls 2.3.5 UV/Visible Spectroscopic Properties of

53

Polymer Systems 552.3.6 Gel Permeation Chromatography 632.3.7 Determination of Metal Incorporation 66

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2.4 Investigation of the Interaction of MetalCarbonyls with Polymeric Supports 67

2.4.1 Photochemistry of Group 6 Metal Carbonyls 682.4.2 Laser Flash Photolysis with UV/Vis

Monitoring 692.4.3 Laser Flash Photolysis Studies of W(CO)g

Toluene Solutions Containing a Polymer-BoundPyridine Ligand 71

2.4 Conclusions 86

CHAPTER 3

Thermal Reactions of Polymer-Bound Group 6Metal Carbonyls When Cast as Films 88

3 . 1 Introduction 88

3 . 1 . 1 Thermal Substitution Reactions of Group 6

Metal Carbonyls 88

3 . 1 . 2 Colloidal Metal Dispersions in Polymers 91

3 .2 Thermal Reactions of Metal CarbonylContaining Polymers 96

3 . 2 . 1 Copolymers of Styrene and M(CO)4-vinylpyridine) 96

3 . 2 . 2 Polymers of Styrene andM(CO)^(4-vinyl-4'-methyl-2,2'-bipy) 10 5

3 . 2 . 3 Thermal Reactions of Polymers of p-Styryldiphenylphosphine 105

3 .3 The Effect of the Chemical Composition of the Polymer Backbone on the Thermal Chemistry 110

3.3.1 The Effect of Changing the Polymer Backbone 110

3 . 3 . 2 Thermal Reactions of Polymers with Free Pendant Pyridine Sites 111

3 . 3 . 3 Effect of Metal Loading 118

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3.4 The Effect of the Physical Properties of the Polymer Backbone on the Thermal Chemistry 119

3.4.1 Effect of Relative Molar Mass on the Thermal Reactionsof Polymer-Bound W(CO)^ species 119

3.4.2 The Importance of the Glass Transition Temperature 124

3.5 Analysis of the Thermal Product of the Decarbonyl ation 131

3.6 Conclusions 133

CHAPTER 4

Preliminary Photochemical Studies of Polymer-Bound Group 6 Metal Carbonyls When Cast as Films 141

4.1 Introduction 142

4.1.1 The Photochemistry of Metal Carbonyl Compounds 1434.1.2 Matrix Isolation in Polymer Matrices 147

4.2 Low-Temperature Photolysis of Polymer-Bound Group 6.Metal Carbonyls 153

4.2.1 A Copolymer of Styrene and W(CO)^ ( vinylpyridine) 1544.2.2 Photolysis of Metal Carbonyl Containing Acrylate

Polymers 1584.2.3 Photolysis of Polymers Containing Metal Tetracarbonyl 161

4.3 Conclusions 164

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CHAPTER 5

5.1 Materials 167

5.2 Equipment and Procedures 167

5.2.1 Infrared and UV/visible Spectral Studies 1675.2.3 Thermal Analysis 1695.2.4 Gel Permeation Chromatography 1695.2.5 Atomic Absorption Spectroscopy 1735.2.6 Photolysis Experiments 1765.2.7 Flash Photolysis of W(CO)^ Toluene Solutions

Containing Pyridine Ligands 17 6

5.3 Synthesis of Monomer Complexes 181

5.3.1 Synthesis of M(CO)5 (vinylpyridine) 1815.3.2 Preparation of M ( C O ) 4 - v i n y l -4 ' -methyl-2 , 2 ' -bipy) 1825.3.3 Synthesis of p-Styryldiphenylphosphine 184

5.4 Preparation of Polymers and Polymer-BoundMetal Carbonyls 187

5.4.1 Preparation of Polymer-Bound Dipyridylmethane 1935.4.2 Anionic Copolymerisation of a-methylstyrene 194

REFERENCES 197

Experimental Section 166

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Acknowledgements

I wish to express my sincerest gratitude and thanks to Dr. Conor Long for his knowledge, humour and supervision over the last three years. I thank my fellow postgraduates, the academic and technical staff for making my time so enjoyable at Dublin City University. I especially thank "The Conor Long Research Group" ( C L R G ) , namley Bernie, Gerry, Barry, Celia and Irene. To my parents and family, whom I could never repay for their love and support, and by no means least my great friends, Jude, Anthony and Damien (AHW). Thank you all.

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Abstract

This work follows the general thrust for the development of hybrid phase catalysts in which the active site maintains the stereochemistry which occurs in homogeneous solution, while the bulk solubility of the material can be controlled by varying the nature of the polymer backbone. In particular, we wish to examine the effect of polymer binding on the chemistry of group 6 metal carbonyls, with a view to the synthesis of polymers in which active coordinatively unsaturated species could be generated, either by thermal or photochemical means.

The polymers of interest contain pendant donor atoms, in particular nitrogen or phosphorus, to which metal carbonyls of the type [M(CO) L ] (M = Cr, Mo, or W; L = vinylpyridine,

6 - n n2,2'-bipyridyl, or p-styryldiphenylphosphine) are anchored. The preparation and characterisation of these materials is discussed. The synthesis of the polymer-bound metal carbonyls can be achieved by two routes. The first involves the preparation of the polymer and subsequent complex forming reaction to bind the metal carbonyl moiety to it. The second pathway involves the synthesis of the metal carbonyl complex containing a polymerisable group which can later becopolymerised with suitable comonomers. The polymer-boundsystems were characterised by UV/visible and infraredspectroscopy. The polymer materials exhibit similarspectroscopic behaviour to their monomeric analogues. The position of the metal-to-1igand charge transfer (MLCT) bands in the UV/visible was found to depend on the nature of the polymer backbone. Laser flash photolysis studies investigating the mechanism and kinetics of binding of the metal carbonyl fragment to the polymer is reported.

The thermal reactions of a variety of the polymer-bound metal carbonyl compounds when cast as films is also presented, as is evidence for the thermal decarbonylation of these materials

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resulting in polymers which contain fully decarbonylated metal centres. Preliminary photochemical investigations indicate the generation of active coordinatively unsaturated metal carbonyl species in polymer matrices at low temperatures.

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AGG J

To my parents.

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CHAPTER 1

AW INTRODUCTION TO POLYMER-BOUND GROUP 6 METAL CARBONYLS

1

1.1 Introduction

In recent years organometal1ic polymers have attracted considerable attention and this interest has resulted in the

1 — 5 •publication of several reviews in this area " . The majority of this research has been concentrated on the attachment of organometal1ic catalysts to organic polymer supports, and indeed a look at the literature dealing with organometallie catalysis reveals the enormous synthetic utility of homogeneous catalysts bound to polymeric matrices.

Anchoring a homogeneous catalyst to a polymer backbone effectively "heterogenises" it, allowing it to function mechanistically as if it were in solution, but physically it would operate as a separate immobile phase. These systems display many of the desirable characteristics indigenous to homogeneous systems, such as catalyst recovery and re-use and high selectivity even under mild conditions. One basic requirement for organometal1ic catalysis by a transition metal complex, is the presence of an open coordination site . Binding a catalyst, which potentially could contain a vacant coordination site to a rigid polymer might permit this molecule to be isolated, thus avoiding non-productive self-aggregation reactions and so affording high concentrations of unsaturated complexes. In this way it is envisioned that the lifetime of highly reactive intermediates could be increased by attaching them to polymeric supports.

2

The concept of binding known homogeneous catalysts to solid phase supports was first introduced by the work of Haag and Whitehurst7 , of Mobil Oil, who demonstrated the catalytic use of salts of Pt(NH ) +2 with polymeric sulfonate counterions and

3 4

later the catalytic applications of heterogeneous species obtained by the coordination of RhCl3 to polymers containing pendant phosphine units8. Since then, work in this area advanced due to the continued efforts of several groups. Further advantages, in addition to ease of catalyst recovery, have been reported for polymer-bound systems. These include enhanced

• . . • » 10ahydrogenation activity of immobilised titanocene and[Ir(C0)Cl(PPh3)2]10b, greater positional selectivity in both hydrogenations10 and hydroformylations1”5, as well as increased selectivity based on substrate size considerations100.

Grubbs et al.2'10a anchored titanocene dichloride to a 20% cross-linked styrene-divinylbenzene (DVB) resin and reduced this with two equivalents of butyl lithium in an attempt to produce a "matrix-isolated" titanocene (Scheme 1). The resulting polymer was 6.7 times more active a hydrogenation catalyst than reduced benzyltitanocene dichloride. These workers also demonstrated the olefin hydrogenation selectivity as a function of substrate molecular bulk afforded by a form of the Wilkinson's catalyst [i.e., ClRh(PPh3)3] , when bonded to a rigid polymer matrix100. They concluded that the catalyst demonstrated many of the best properties of both homogeneous and heterogeneous catalysts and in addition, were capable of selecting olefins from solution on

3

the basis of their size, the rate of reduction being dependant on the molecular size of olefin. In a similar work11, Grubbs et a l . showed that polymers may exert polar selectivities as well as those based on size. Polystyrenes (1-2% DVB) swell less in polar solvents so that ethanol decreases pore size and increases diffusional restrictions, thus the rate of cyclohexene reduction increased upon changing the solvent from benzene to 1:1 benzene-ethanol. Despite a reduction in swelling, a polar gradient is established which favours a higher concentration of the alkene within the resin when ethanol was used. These findings had not only demonstrated that these heterogenised anchored systems could perform as well as their homogeneous counterparts, but also that the polymer matrix could play an important role in determining the outcome of catalysis.

4

Polymer-supported catalysts also exhibit selectivities when used as hydroformylation catalysts1”5'12-16. Phosphinated polystyrene (PS) cobalt catalysts of the type [PS-PPh2Co(CO)3]2 gave complete conversion of 1-pentene to the appropriate aldehyde in 96% selectivity (4% pentane) at 150°C and 68 atm Hz/C016. Compared with the homogeneous catalyst, the normal to branched ratio (n/b) was 2, close to that of the unbound analogue. More alcohols were produced over 150°C and the n/b ratio dropped to 1.4. This is lower than that of the unbound catalyst (n/b=3), Co2(CO)2(PPh3)z.

Pittman and Smith12 put forward the first examples of sequential multistep organic reactions in which two catalysts,[(PPh ) Ni (CO) ] and [(PPh ) RhCl ] , were bound to the same

3 2 2 3 3

crosslinked polystyrene backbone. They described the sequential cyclooligomérisation-hydroformylation of butadiene in which the product of the first reaction (vinylcyclohexene) is "fished out" by the second very selective hydroformylation of a terminal double bond. The aldehydes are readily separated from theremaining products. Butadiene was first cyclooligomerised quantitatively to cyclooctadiene, 1,5,9-cyclododecatriene andvinylcyclohexene by the supported nickel carbonyl. The supported rhodium catalyst was highly selective in catalysing thehydroformylation of the only terminal double bond in the products (vinylcyclohexene). The two catalysts can be attached to the same resin, or to two separate resins which may be subsequently mixed in the reactor. These experiments illustrated

5

that the two bound catalysts behaved as they do individually, and that reaction of the two mixed catalysts with each other was avoided because contact between them was prevented by anchoring to the rigid supports.

While having enormous utility in the field of organometal1ic catalysis, the number of potential applications in which the use of metal-containing polymers can be considered is wide. Areas of application4 currently under investigation include a) catalysis, b) thermally stable materials applications, c) biological applications (antifungal agents and insecticides), d) biomedical applications (antibacterial, controlled release, antiviral, antitumoral), e) additives (coatings, paper, plastics), f) electrical applications (conductors, semiconductors), g) photoactive materials (xeroxing type applications), h) analytical applications, i) flame retardants, j) nonlinear optical devices, and k) preparation of ceramics. These examples illustrate the applications and importance of the many and varied metal-containing polymer systems. An excellent and comprehensive review on the above applications has been published by Pittman and Carraher4.

A number of organometallie metal carbonyl containingpolymers have been investigated. Many metal carbonyl complexesof group 6 and 7 metals have been reported to catalyse well

1.7known reactions such as isomérisations , hydrogen shift reactions17, hydrogenations17'19, dimérisations17, oligo­

6

merisations20, alkylations and acylations21, and olefin metathesis22'23. As a result, many of their polymer-bound analogues have been reported.

17 24 25Metal carbonyl complexes undergo many photochemical and thermal24'26 reactions. Indeed, metal carbonyls are among the most thermally and photochemically labile range of compounds so far investigated. Hence, thermal and photochemical reactions of metal carbonyls have found wide applications for synthetic purposes. Thermolysis or photolysis can result in the production of coordinatively unsaturated species and so consequently, the generation of these reactive species in polymer-anchored systems is of particular interest. The high extinction coefficients of metal carbonyl complexes in the ultraviolet and infrared regions of the spectrum facilitate their study, and polymer supports can be chosen to be transparent in the region needed for spectral examination. The availability of a large data base for the systems makes them ideal for further investigation.

Many transition metal carbonyl containing organic polymers have been prepared. Example classes include polymers where the metal is (a) bound by phosphine or nitrogen ligands ,(b) «-bonded to aryl ligands52-56, (c) chelated as coordination

30 32complexes ' , or (d) attached to the matrix by ac p C Ocarbon-to-metal a-bond ' . These methods of bonding the metal

carbonyl complexes to polymers provide convenient routes to the incorporation of transition metal carbonyl moieties into polymers. Some examples of each class will be discussed.

7

Phosphine ligands have received the most attention as modes of attaching transition metal complexes to polymer supports2. As a result of the wide variety of known transition metal organometal1ic species containing coordinated phosphines, a vast array of polymer-bound catalysts may be envisioned in which the active metal is directly coordinated to a polymeric phosphine ligand. In many catalytic reactions loss of a phosphine ligand is an important step, and so has important consequences in hybrid system design for these complexes. Numerous metal

32carbonyl derivatives have been formed from phosphine ligands Group 6 carbonyl complexes with phosphine ligands are usually synthesised using standard substitution reactions; (1)displacement of CO from M(CO) aided by heat and/or UV light,

6

(2) displacement of one or more weakly bonded ligands fromcarbonyl derivatives, also usually aided by heat and/or UV lightand (3) direct combination of the phosphine ligand and M(CO) in

6

a sealed tube. These methods can be employed in the preparation of polymer-anchored systems.

Polymeric phosphine ligands have have been synthesised in most reports by functionalisation of a preformed polymer. Examples include the preparation of the polymeric analogue of triphenylphosphine by the lithium diphenylphosphide-bromine

3 3 - 3 5route " (I), and the preparation of polymeric analogues ofbenzyldiphenylphosphine by the reaction of lithium diphenyl phosphide (LiPPh2) with the correspondingchloromethylated polystyrene (II)8,36'37. Alternatively, the

8

phosphine containing monomer may be prepared and then copolymerised38"44 (III) (see Scheme 2). The method used will depend on the desired properties of the polymer, but because of the availability of polystyrenes with a wide range of crosslink densities, narrow molecular weight distributions, and surface areas and porosities, methods I and II have received most attention.

9

Pittman16 examined a large number of reactions of metalcarbonyls with polymeric analogues of bothbenzyldiphenylphosphine and triphenylphosphine in terms of theextent of metal incorporation onto linear and cross-linkedpolymers and the properties of several of these species ascatalysts in organic reactions. The compounds M(CO)" 6(M = Cr, Mo, or W), cyclopentadienylmanganese tricarbonyl(CpMn(CO) ) and Mn (CO) were reacted with the polymeric' ' 3 2 10ligands to produce the bound metal carbonyls via carbonylsubstitution reactions. The two metal phosphines compounds, [(PPh ) Ni(CO) ] and [(PPh ) RhCl ] , were bound to the

3 2 2 3 3

cross-linked polymeric ligands by phosphine exchange reactions. These and other phosphine bound metal carbonyls investigated are illustrated in Scheme 3.

In all the systems studied the reactions of the metalcarbonyls with the polymeric ligands were found to proceed smoothly in a manner not unlike the reactions between the metal carbonyls and monomeric phosphines. Both the linear and the cross-linked resins were found to be reactive and a high percentage of metal was incorporated onto the polymers based upon the available phosphine present. Reactions of M(C0)

6

(M = Cr, Mo, or W) with polymer-bound benzyldiphenylphosphine were carried out both thermally and photochemical 1y , both proving to be equally efficient in incorporating the metalcarbonyl. The polymers were characterised by their infrared spectra and the CO stretching frequencies were similar to the

10

11

related monomeric derivatives. Although the reactions were carried out using a molar excess of the metal carbonyl compound, the CO stretching spectra of the resin-bound derivatives of the group 6 hexacarbonyls indicated that significant amounts of trans-disubstituted derivatives had formed. This observation indicates a high degree of mobility of the coordination sites within the matrices containing a low degree of cross 1 inking.

Cais et al?7 treated chioromethylated styrene- divinylbenzene resins with lithium diphenylphosphide to produce resins containing bound pp^2 groups. A photochemical substitution reaction with phenanthrenechromium tricarbonyl yielded polymer attached phenanthrenechromium dicarbonyl units (see Scheme 3). They investigated the catalytic activity of this system in the hydrogenation of dienes. Mechanistic studies indicated that if the Cr(C0)3 groups were attached directly to the phenyl rings the group would be leached into solution by coordinating solvents used in the reaction. Anchoring of arenechromium carbonyl complexes by a phosphine ligand covalently bound to the polymer would prevent leaching of the chromium moiety into solution in the course of the reaction. Scanning electron microscopy (SEM) showed that chlorométhylation proceeded uniformly throughout the polymer beads, while phosphination and the photochemical reactions behaved differently, depending on the macrostructure and morphology of the polymer beads. It was discovered that polymers with large pores (1300A) allowed the reagents (phosphine and chromium

12

complex) to react throughout the polymer beads, while in

polymers with small pores (<50A), penetration was limited.

In another study, Sanner and coworkers described the preparation and photocatalytic activity of a Fe(CO)^ (n = 3 or 4) species bound to a styrene-divinylbenzene resin via a triarylphosphine anchor45. A key question concerning the use of polymer-anchored catalyst precursors concerns the photostability of the anchoring bond. In this instance the question posed was whether photoexcitation of [POL-PPh ] Fe(CO) will break Fe-P

2 5 - n n

bonds or result in CO expulsion. Results for photocatalysed alkene isomérisation and alkene reaction with trialkylsilane using the polymer-anchored system were very similar to results found by using [Fe(CO) PPh ] and [Fe(CO) (PPh ) ] in homogeneous

4 3 3 3 2

solution. The photocatalytic activity was attributable to the photogeneration of coordinatively unsaturated iron carbonyl species which then follow a mechanism similar to that of Fe(CO) 46, with the perturbation of having triarylphosphine in

5

the coordination sphere. Thus, irradiation of [Fe(CO) (PPh ) ]3 3 5 - n

(n = 4) resulted in loss of CO not PPhg, suggesting a photoinert anchor to the Fe(CO) groups in the polymer matrix. Thesenexperiments established the viability of photogenerating catalysts anchored to polymer supports without destruction of the anchor bond in the photogeneration procedure.

Polyvinylpyridines have been complexed with a large number of metal salts and complexes. Examples3 include Cu(OAc)z

13

complexes used as H 2 ° 2 decomposition catalysts, Mn(II) phthalocyanine complexes and other Cu(II) salts. Metal carbonyl complexes of pyridine and substituted pyridine are easily prepared by substitution reactions by thermal or photolytic

3 2means, and have been the subjects of many studies . Thesynthesis of anchored group 6 metal carbonyls has been achievedby reaction with polymer-bound pyridine. Biedermann48 firststudied the substitution reactions of chromium and tungstenhexacarbonyls with poly-4-vinylpyridine. He reported thatheating M(CO) (M = Cr or W) and 4-vinyl pyridine (L) in an

6

evacuated autoclave gave [ML CO] , [ML ] , [ML (CO) ] , and5 n 6 n 3 3 n

[ML (CO) ] . The complexes were characterised by their infrared4 2 n

spectra. Simultaneous polymerisation of L occurred during thereaction.

Moffat47 reported the use of pol y-2-vinylpyridine to support cobalt carbonyls. Since cobalt carbonyls attached topyridine, triphenylphosphine, and other coordinating groups catalyse hydroformylations, Moffat proposed that polymers containing these groups might also do so. He found that poly-2-vinylpyridine can be used, but its behaviour is not quite what one would expect. Polymers of little or no crosslinking may be soluble under hydroformylation conditions but at high crosslinking the solubility is very low. At intermediate levels the polymer swells, but does not dissolve. With 4 to 8% DVB crosslinking, some of the catalytic portion of the molecule escapes into the solution and carries the reaction forward. The

14

concentration of cobalt in the reaction medium under reaction conditions in Moffat's experiment was 100-300 ppm. Upon coolingand admission of H and CO, the concentration fell to less than

2

10 ppm. He found that the cobalt carbonyl species are released from the the solid polymer phase, depending on the presence or absence of hydrogen. Thus surprisingly, the polymer acted as a catalyst reservoir.

The synthesis, spectroscopic, chemical and photochemical properties of M(CO) (M = Cr, Mo, or W) complexes of 2- and

5

4-vinylpyridine (4-VP) and their copolymers with vinylpyridines,2 9styrene and methylmethacrylate have been studied . It has been

known that the efficiency of an organometal 1 ic catalyst can be greatly enhanced by UV irradiation and that the possibility exists for both generation and regeneration of the catalyst by this means. The [W(CO) (substituted pyridine)] was a

5

particularly well characterised system17,24,25. It seemed therefore, that a study of M(CO)s complexes of polyvinylpyridine might prove useful in determining how the photoprocesses of a substituted metal carbonyl are affected by binding to a polymer and in seeing whether the photochemical properties of the complex can be "tuned" by systematic variation in the polymer backbone. The metal carbonyl containing polymers were synthesised either by reaction of photochemically generated [M(CO) (ethanol)] with a preformed well characterised homopolymer or copolymer of vinylpyridines (VP) or alternatively, by preparing the [M(CO) (VP)] complex and

5

15

copolymerising it with other vinyl monomers. The results reported indicated that M(CO) (4-VP) complexes have properties similar to those of other pyridine substituted metal pentacarbonyl species. However, 2-vinylpyridine complexes were unstable and this instability was probably attributable to the steric interaction of the M(CO) group and the vinyl group. It

5

was found that M(C0)s(4-VP) readily copolymerised with other vinyl monomers. Preliminary results indicated that the energy of the metal-to-1igand charge transfer band in the UV/visible is sensitive to the nature of the polymer backbone, shifting to lower energy when vinylpyridine replaces styrene in the polymer chain. Photocleavage of the W - N bond was found when W (CO) (VP)-copolymers were irradiated at X = 436 nm and the

5

relative quantum yield for photodissociation in styrene-4-vinylpyridine-W(CO) (4-VP) terpolymers was dependent

5

on the nature of the polymer backbone and in particular, on the proportion of uncoordinated vinylpyridine groups on the chain. These observations confirmed the view that it should be possible to "tune" the photochemical properties of organometal1ic compounds by binding them to polymers and so develop more effective photocatalysts.

The chelating ligand 2,2'-bipyridine (bipy) has been used to attach metal carbonyls to polymer matrices49. Card and Neckers reported the synthesis of a crosslinked polystyrene-based bipyridine system and discussed some of it's physical, chemical and catalytic properties. One of the

16

potential advantages of a polymer-bound chelating ligand is the expected decreased lability due to the chelation effect6. The ligand was attached to the polymer backbone by reaction with the lithiated phenyl residues (see Scheme 4). Zerovalent metal carbonyl complexes such as [POL-Ph-bipy-M(CO) ] (M = Cr, Mo, or4

W) were readily prepared by refluxing with the parent hexacarbonyl.

n— BuLiBr Bipy2 THFPOL-Ph —r—z— ► POL—PhBr ------ ► ► POL-Ph-BipyAlCl. o3 0 C-RT reflux,air

Cr(CO)6hy or A

POL— Ph-BipyCr(CO) + 2CO <■4 THF

Scheme 4A number of research groups have investigated transition

metal carbonyl rc-complexes bound to polymers. The preparation of vinyl monomers containing 7t-bonded metal carbonyls has received considerable attention. Rausch and Moser were the first to report the successful synthesis ofrj6-(styrene)chromiumtricarbonyl (III)50. They reported that the reaction of styrene and triamminechromiumtricarbonyl in refluxing dioxane gives the desired vinyl metal carbonyl in 50-60% yield, while synthesis v i a a Wittig reaction involving benzaldehydechromiumtricarbonyl gives an improved yield of 83% (Scheme 5). Synthesis from chromium hexacarbonyl and styrene by

5 1methods analogous to those of Nicholls and Whiting was unsuccessful producing only polystyrene and green chromium

17

salts. Studies suggested that (III) undergoes polymerisation less readily than does styrene itself. Attempts to polymerise (III) in degassed toluene at 60-80°C using azobisisobutyronitri1e (AIBN) as the initiator failed. Under these same conditions styrene polymerises readily. However, thermal copolymerisation of styrene and (III) afforded the desired copolymer, identified by IR spectroscopy.

Pittman52, in the first of his many detailed investigations into the reactivity of vinyl metal carbonyl monomers, probed the reactivity of the radical (IV) in copolymerisations with styrene

and methyl acrylate. The values for the reactivities were found to be small, indicating that radical (IV) does not add (if at all) to (styrene)chromium tricarbonyl. This agreed well with the

observed inability to homopolymerise this monomer. Radical (IV) readily adds to styrene and methyl acrylate, and also styryl and

18

methyl acrylate radicals readily add to (III). The 7t-Cr(CO ) 3

moiety has a strong electron withdrawing effect, but it supplies electron density to adjacent centres of electron deficiency by resonance or a direct interaction mechanism. The ability of (IV) to add readily to both styrene and methyl acrylate, suggests that a steric effect might be preventing the addition of (IV) to (III). (Styrene)chromium tricarbonyl (III) was successfully copolymerised with styrene and methyl acrylate and with5 52r7 -(vinylcyclopentadienyl)manganese tricarbonyl (Scheme 6 )

The copolymers were characterised by infrared spectroscopy.

An alternative route to (styrene)chromiumtricarbonylpolymers is the reaction of polystyrene with chromiumhexacarbonyl by refluxing in dimethoxyethane according toscheme 7. Pittman et a1 . used this polystyrene-anchored chromiumtricarbonyl in the hydrogenation of methyl sorbate52c. Theyfound that the product distribution was different from that of aknown homogeneous hydrogenation catalyst for methyl sorbate.They assigned this difference to diffusion into the polymerbeads being a rate-limiting factor. Similar molybdenum andtungsten tricarbonyl polymers were synthesised by reacting theprepared tris-acetonitri1 e tricarbonyl complexes withpolystyrene since the rate at which Mo(CO) and W(CO) react

6 6

with aryl rings to give the respective rc-compl exes is muchslower than that with Cr(CO) .

6

19

2 , X

Mn(CO).

/

■(CH CH)—

Mn(CO).

Scheme 6

20

Pittman and coworkers investigated other rj -metal carbonyl0vinyl monomers. The monomers rj -(2-phenyl ethyl acrylate) chromium

5 3 6tricarbonyl (V) and rj -(benzyl acrylate)chromium tricarbonyl(VI)54 were synthesised and copolymerised in solution at 70°Cwith styrene, methyl acrylate, acrylonitrile and 2-phenyl ethyl acrylate in ethyl acetate, AIBN being used as the radicalinitiator. A homopolymer of (V) and copolymer of (V) with styrene were decomposed under the influence of UV and visible light. The CO stretching bands in the infrared disappeared with continued exposure to light. The polymers were found to containCr2°3 (Scheme 8). Thermal decompositions were also conducted.These also resulted in decomposition of r]6-(aryl )Cr(C0)3 units to produce mixed oxides embedded in the highly crosslinked polymers.

0

In a succeeding paper, Pittman reported decomposition experiments of siloxane polymers to which transition metal carbonyls had been re-bonded to the aryl rings55. Two siloxanepolymers were chosen for complexation with Cr(CO) . One of the

6

21

siloxane polymers prepared, containing an in-chain phenyl substituent, is illustrated in Scheme 9. Thermal analysis indicated the loss of CO at 200°C and subsequent freeing of tiny chromium oxide particles within the polymer matrix.

conjugated organic polymers having chromium carbonyls coordinated to the polymer backbone. He reported an efficient means of preparing conjugated polymers v i a the palladium-catalysed polycondensation of group 6 arene complexes with organostannane compounds (Scheme 10). Thermolysis of these polymers resulted in weight loss and changes in the infrared spectrum due to CO loss. Combustion analysis data and differential scanning calorimetry were consistent with carbon monoxide loss at the chromium metal centres followed by some form of cross-linking. A similar change in the infrared spectrum can be obtained by irradiating the polymer. Thermogravimetric analysis in air shows a break point of 381°C and rapid weight loss to give Cr 0 .

2 3

22

One of the first organometal1ic carbonyl polymers prepared was reported by Cais57, and involved the thermal polymerisation of rj5-(cyclopentadienyl )manganese tricarbonyl (VII) during the dehydration of (1-hydroxyethyl)cyclopentadienylmanganesetricarbonyl over KHSO^ (Scheme 11). The polymerisation proceeded easily at 170°C to give an orange glassy polymer which softened at 80°C. This polymer was recommended as an additive to liquid and solid fuels as a combustion catalyst.

23

Following this brief report, Pittman's group became the first to conduct a detailed study of r]5-CpM(CO)3 containing polymer systems. Vinylcyclopentadienylmanganese tricarbonyl(VII) has been readily copolymerised with styrene, methyl acrylate, aery1onitri1e , vinyl acetate and vinyl ferrocene in benzene or ethyl acetate at 70°C using azobisisobutyronitrile (AIBN) radical initiation (Scheme 12)58. The polymers were characterised by gel permeation chromatography (GPC) and infrared spectroscopy. The reactivity ratios were determined. It was found that transition metal carbonyl functions, when attached to a vinyl group, exert large effects on the addition polymerisation reactivity. These organometal1ic monomers exhibit very electron-rich vinyl groups in radical polymerisations. In another study, the same group synthesisedrj5-(vinylcyclopentadienyl)dicarbonylnitrosyl chromium (VIII) and copolymerised it in solution with styrene and

5 9N-vinyl-2-pyrrolidone . They demonstrated that changing the metallic fragment from Mn(C0)3 to Cr(CO)2NO did not effect the

<§ r J > ■K\ BN

CH =CHX — =-r— i2 AMn

( C O ) .

0II

0II

■ (CH C H ) — (CH C H ) — 2 x 2. y

0

Mn(CO).

n

X= Ph-,CH.OC-,-CN,CH CO- , F e r r o c e n e.»5 <3

Scheme 12

24

reactivity of the vinyl group. Copolymers of (VIII) were shown to catalyse the selective 1,4-hydrogenation of methyl sorbate. The potential biological activity which monomer (VII) might impart to polymer coatings was investigated and the films formed were found to exhibit fungal resistance in accelerated growth tests.

N-vinyl-2-pyrrolidone is a versatile monomer with usefuladhesive properties. It's homopolymer is water soluble and formshard, transparent films which are strongly adhesive to smoothsurfaces. These properties, and the added advantage that it isinert toxicological1 y , mean that it finds great utility in theformulation of paints. With these properties in mind, Pittmancopolymerised N-vinyl-2-pyrrolidone with (VII) to investigate ifthe presence of manganese and it's polar carbonyl groups might

6 0lead to useful adhesive properties . The resulting copolymers were readily soluble and exhibited excellent adhesive properties. Thermal decompositions were carried on the copolymers and upon heating, carbon monoxide evolution was noted with corresponding weight loss, until at 280°C a dark insoluble

(VII) (VIII)

25

polymer with no CO bands in the infrared remained. The decrease in solubility, it was suggested, resulted from crosslinking by cyclopentadienyl dimerisation. Also free manganese oxide distributed throughout the polymer would result in decreased solubility and darkening.

Tricarbonyl hydride derivatives of cyclopentadienyl chromium, molybdenum and tungsten compounds were covalently linked to highly crosslinked polystyrene (PS) supports by Brintzinger and Gubitosa61. Treatment of polystyrene-attached cyclopentadienyl anions with the respective metal hexacarbonyl and subsequent acidification gave (PS) -CH^-^H^MiCOj^H (M = Cr, Mo or W). The thermal stabilities of the polymer-supported cyclopentadienyl tricarbonyl hydrides, particularly those of chromium and molybdenum, up to temperatures close to the melting point of the polymer matrix contrasts sharply with the thermal instability of C H Cr(CO) H and C H Mo(CO) H. These compounds

5 5 3 2 5 3

are known to lose H at temperatures of about 50°C with formation the binuclear species [C H Cr(CO) 1 , while the

5 5 3 2

polymeric materials undergo decompositions with loss of H and2

CO at much higher temperatures of about 200-210°C.

The use of metal carbonyl anions give particularly convenient routes to incorporate transition metal carbonyl moieties into polymers. Metal carbonyl anion chemistry provides facile routes to polymers where the organometallie group is fixed to the polymer via pendant a carbon-metal bonds. Treating

2 6

chioromethylated polystyrene resins with NaMn(CQ) , introduced' 5g opendant [POL-C H CH Mn(CO) ] functions in polymers . Thermal6 4 2 5

decomposition at 140°C released Mn (CO) within the matrix. In2 10

another paper the synthesis and thermal decomposition ofrj1-benzyl-r)5-cyclopentadienylmolybdenum tricarbonyl (IX) (and tungsten (X)), and their linear and crosslinked polymers[POL-C H CH M(C0) (C H )] to which (IX) and ( X ) have been

6 4 2 3 5 5

affixed were discussed63.

“ ¡ 7 N " v i s .

( I X ) (X)

The metal carbonyls, (IX) and (X), were attached to the polymer by reacting the chioromethylated polystyrene with either excess Na+[Mo(CO) C H ]” or Na+[W(C0) C H ]" to generate the3 5 5 3 5 5

desired polymer (see Scheme 13). Thermal studies of (IX) and (X) were carried out in solution and neat. Carbon-metal bond cleavage was followed by collapse to dimer. Large amounts of benzyl migration to the cyclopentadienyl rings occurred. The polymers decomposed more rapidly in solution than neat as larger amounts of dimer were recovered in solution decompositions. It was proposed that in the absence of solvent, carbon-metal recombination would be more efficient since the polymers were

27

solid and radicals would be expected to have lower mobility. In solution, the [ C H M ( C O ) ]' radical would have sufficient

5 5 3

mobility to allow radical combination reactions to produce dimeric species. The tungsten polymers decomposed more slowly than their molybdenum analogues in agreement with the well established increase in metal-carbon bond strengths moving from Cr to Mo to W.

The main growth in the research of attaching an organometallie transition complex to an organic polymer backbone arose from the greatly improved and easy separation of expensive anchored catalysts from reaction mixtures. It later became clear that the support could play an even more important role other than improving catalyst separation. Not only was it found that these "heterogenised" systems could perform as well as their homogeneous analogues, but by varying the composition of the polymer backbone one could introduce selectivities based on the

28

properties of the support. So the outcome of a catalytic reaction can depend as much on the polymeric support, as on the bound catalyst. Selectivities have been induced in polymer-bound systems simply by changing the crosslink density. The number of polymers available which can be used to attach transition metal complexes is enormous and the different inherent properties of these polymers can be used and chosen to ones advantage. The vast majority of work in this area has been involved in the area of organometallie catalysis and because of the interest this topic generates, numerous comparisons with the known homogeneous systems have been conducted. Organometal1ic catalysis is not the only area these materials find applications. Reports have appeared acknowledging their use in a wide variety of applications including uses in electronic and biomedical applications.

Transition metal carbonyls can be easily attached to polymer supports with high degrees of metal incorporation. Many vinyl containing metal carbonyl complexes have been synthesised and both homopolymerised and copolymerised with widely available comonomers. The intense absorptions of metal carbonyls in the infrared make them easily characterisabl e . The ease with which metal carbonyls undergo photochemical and thermal reaction make them ideal for investigation due to the wide number of photochemical, spectroscopic and thermal techniques available for their study. A great deal of research is performed in the field of metal carbonyl chemistry every year, so the potential

29

number of analogous polymer-bound related experiments is enormous. Metal carbonyl incorporation into polymer backbones is achieved relatively easily, in one step reactions in most instances. However, a look at the literature illustrates just how little work has been done into this area. Much of theresearch concentrates on their use, not surprisingly, as polymer-bound catalysts. Another area of interest is the thermal decomposition of metal carbonyl moieties to free metals, metal oxides or organometal1ic carbonyl groups within polymericmatrices.

This thesis is concerned with the preparation of a series of polymer-bound group 6 metal carbonyl compounds and the examination of the effect of polymer-binding on the chemistry of the metal carbonyl moieties. This work has as it's general aim the synthesis of polymers in which active coordinatively unsaturated species could be generated, either by thermal orphotochemical means. The work follows the general thrust for the development of hybrid phase catalysts in which the active site maintains the stereochemistry, which occurs in homogeneous solution, while the bulk solubility of the material can becontrolled by varying the nature of the polymer backbone.

30

CHAPTER 2

THE SYNTHESIS AND CHARACTERISATION OF POLYMER-BOUND

GROUP 6 METAL CARBONYLS

31

and tetracarbonyls are rare. The photochemistry of these metal carbonyls, and to a lesser extent the thermal chemistry, of these metal carbonyls is well known and documented. It seemed likely then, that the polymer bound analogues would be photochemical 1y and thermally reactive also, but the effect the polymer backbone might have on these reaction routes was of interest.

The syntheses of suitable polymerisable ligands and metal carbonyl containing systems and the polymerisation, identification and characterisation of appropriate copolymers will be discussed in this section. Laser flash photolysis studies investigating the mechanism and kinetics of binding of the metal carbonyl fragment to the polymer backbone will also be presented. The experimental details of syntheses and procedures employed are presented collectively in section 5.

2.2 Preparation of Polymer-Bound Metal CarbonylsThe polymers of interest contain contain pendant donor

atoms, in particular nitrogen or phosphorus. The synthesis of polymer-bound metal carbonyls of this type can be achieved by two routes. The first route involves the preparation of the polymer and subsequent complex forming reaction to bind the metal carbonyl moiety to it (Scheme 14a). The second pathway involves the preparation of the metal complex containing a polymerisable group which can later be copolymerised with suitable comonomers producing the desired polymer-bound complex

3 3

routes. Using the first route (Scheme 14a), the polymer can be fully characterised before complex binding. However, during the complex forming reaction it is possible that not every site on the polymer backbone will coordinate to a metal centre (eventhough a 1:1 ratio of W(CO) moieties to pendant sites on the

5

polymer is used). In the latter case (Scheme 14b), every pendant site is coordinated to a metal centre because the metal carbonyl was reacted with a polymerisable ligand, purified and thencopolymerised so that the loading of metal carbonyl complex in the polymer backbone is known. Unfortunately these polymer systems are difficult to characterise. Both of these methods were utilised in this work, depending on the particular properties required of the polymer.

The metal carbonyl complexes were bound to the polymer supports by reaction with [M(CO) (tetrahydrofuran)] (M = Cr, Mo,

5

or W) in tetrahydrofuran (THF) at the required concentration. The [M(CO) (THF)] species is generated by photolysis of the

5

parent hexacarbonyl , M(CO) , in THF17’24’25.6

M(CO) + S ---- ^ ----> M (CO) S + CO6 N 5

2

M(CO) S + L -----------> M(CO) L + S5 5

M = Cr, Mo or W S = SolventL = Monomer or polymer containing a pendant donor atom.

(Scheme 14b). Advantages and disadvantages exist for both

Scheme 15

34

Irradiation of M(CO) in a weakly coordinating solvent such as6

THF in the presence of an incoming ligand, proceeds by astabilised transition state to give an observable [M(CO)5S]intermediate. The addition of L then gives the product by facile replacement of the coordinated solvent molecule.

In this study, all the monomer and polymer metal carbonyl complexes were prepared by the same above route involvingreaction with [M(CO) (THF)]. The solvent adduct [M(CO) (THF)] is

5 5

generated as a clear yellow solution by photolysis of M(CO) in6

freshly distilled THF under a continuous nitrogen purge, and added to a solution of the monomer or polymer in THF. Thesolvent is then removed under reduced pressure, the THF being displaced from the metal complex by the pendant moieties on the polymer backbone to form the desired metal carbonyl system. In the instance of polymer or monomers containing bipyridyl (bipy) binding sites, an additional thermal decarbonylation occurs during the preparation to give the tetracarbony1 species.

W(CO) S + bipy5

A W(CO) (bipy) + S5

W(CO) (bipy)bA W(CO) (bipy) + CO

4

35

36

ROUTE 2

Formation of the metal carbonyl complex containing a polymerisable group followed by copolymerisation of complex with suitable comonomers.

ML + L ► ML , L + Lx x - t

CO-MONOMER

IML . L ----x - i

POLYMERCHAIN

FOR EXAMPLE

W(CO)c + THF --^ W(CO) THF + CO6 5W(CO) THF + 4-VP ------ ► W(CO) (4-VP) + THF5

VP = vinylpyridine

37

The ligands/monomers of interest 4-vinylpyridine (XI), 2-vinylpyridine (XII), 4-vinyl-4'-methy1-2,2'-bipyridyl (XIII), and p-styryldiphenylphosphine (XIV) are illustrated below. The vinylpyridines (XI) and (XII) are commercially available, (XIII) was synthesised according to the method of Ghosh and Spiro32b, while (XIV) was prepared by Grignard synthesis from

3 8p-bromostyrene and chlorodiphenylphosphine . Each monomeric ligand contains a donor atom (nitrogen or phosphorus) and a polymerisable vinyl group. These ligands readily replace carbon monoxide from metal carbonyl complexes (see Scheme 15 above) and yield stable complexes which survive polymerisation reactions using AIBN as the radical initiator.

substituted pyridine, are particularly well characterised and have been the subject of many photochemical

16 2 4 2 5investigations ' ' . Pyridine is a ligand with good donorability, and it and it's substituted derivatives are the most common type of a-donor nitrogen ligands found in metal carbonyl compounds, although reports of similar polymer-bound systems are

38

rare. Homopolymers and copolymers of vinylpyridines containing bound M(CO) moieties have been previously investigated as

5

potential photocatalysts, and the effects of the polymer• 2 9backbone composition on the observed photochemistry discussed

The bidentate nitrogen ligand 2,2'-bipyridyl, has been the topicof many studies64. Potentially bidentate nitrogen ligands (L-L)can act as chelating ligands or as bridging ligands ifgeometrical constraints preclude chelation. Many of the studiesof chelation reactions have been carried out with oc-diimineligands such as 2,2'-bipyridyl. The chelation processes of suchligands at metal hexacarbonyl centres, particularly Cr(CO) ,

6

have been investigated. The efficiency of bipyridyl and other diimine ligands is due to both their chelating ability and a balance between their cr-donor and re-acceptor properties. The ligand 4-vinyl-4'-methyl-2,2'-bipyridyl (XIII) and similar vinyl monomers have been copolymerised and used to anchor ruthenium complexes and tungsten tetracarbonyl complexes for use as

fi Velectrode coatings . In other papers, 2,2'-bipyridyl has been attached directly to polystyrene polymers from the reaction of lithiated polystyrene with bipyridyl in THF and used to complex

■ 3 Ochromium tetracarbonyl and palladium complexes

Group 6 carbonyl complexes with monodentate phosphorus ligands are usually synthesised using standard substitution reactions. The phosphorus atom has a lone pair of electrons available for a-donation, as well as an empty 3dre orbital of the appropriate symmetry and energy to accept electron density from

3 9

the metal in a re-bonding interaction. Although amines are better a-donors than trivalent phosphorus compounds, the jt-acceptor capability of the phosphorus ligands makes them effective as ligands in complexes of metals in low oxidation states. In general, the greater the electronegativity of the substituent on the phosphorus atom, the poorer the basicity of the lone pair, and the poorer the a-donation. Many monomeric phosphines of the

65type [M(CO) (PPh )] have been synthesised and characterised5 3

Phosphine ligands have received most attention in the area ofpolymer-bound organometallie complexes and have been widely usedas anchors to attach organometal1ic transition metal complexesto polymeric supports33-37. Polymers containing phosphineligands have been prepared either by functionalisation ofpreformed polystyrenes or by copolymerisingp-styryldiphenylphosphine (XIV) with suitable comonomers,followed by subsequent complex forming reaction. Pittman et

16a 1. attached group 6 metal carbonyls to a crosslinked polystyrene support containing diphenylphosphino ligands by both thermal and photochemical means. Polymer-bound phosphines have also found utility as polymeric reagents in Wittig olefin synthesis66.

The monomers of interest were either copolymerised with suitable comonomers (Scheme 14a) and then reacted with [M(CO) (THF)] to give the polymer-bound metal carbonyl or,

5

firstly reacted with [M(CO) (THF)] to give the functionalised5

monomer and then copolymerised (Scheme 14b). Copolymerisations

40

were carried out by free-radical polymerisation at 70-80°C in the absence of solvent under a nitrogen atmosphere, usingazobisisobutyronitri 1 e (AIBN) initiation. The polymerisations all proceeded in good yield, and the polymers were readily purified by repeated precipitation from chloroform by petroleum ether.

2.3 Characterisation of Polvmer-Bound Metal Carbonyl SystemsA number of techniques are available for the study and

characterisation of these materials. Spectroscopic techniques have been invaluable in the study of group 6 metal carbonyls and their derivatives, but in these systems one can utilisetechniques employed for the analyses of polymers also, and apply them to the polymer-bound metal carbonyl materials. In the following sections, infrared and UV/vis spectroscopy, elemental analysis and gel permeation chromatography (GPC) are discussed with particular regard to the characterisation of thesepolymeric materials.

2.3.1 V i b r a t i o n a l S p e c t r a o f M e t a l C a r b o n y l s .

Infrared spectroscopy is widely used in the study of metalcarbonyls since the CO stretching frequencies give very strong sharp bands (e up to 10,000) well separated from othervibrational modes of any other ligands that may also be present. CO is a very weak electron donor and the principal process which holds the CO onto the metal is back-bonding . Thus the bonding in metal carbonyl compounds involves a dative overlap of filled carbon a-orbital and 3d cx-orbitals of the metal, and a dative

41

overlap of a filled 3dir metal orbitals with empty pn orbitals of the CO. As CO "pushes" electrons onto the metal atom, the metal can off-load the increased electron density into the

& An orbital in CO. So the n antibonding orbital in CO ispartially populated. The effect of this back-bonding is toincrease the M-C bond strength while reducing the strength ofthe C-0 bond. Therefore, the carbonyl stretching frequency (^ )of CO decreases on binding to the metal. The CO molecule has astretching frequency of 2143 cm”1 in the gas phase, whileterminal CO groups in neutral metal carbonyl molecules are foundin the range 2100 to 1800 cm"1, showing the reduction in CO bondorders. Moreover, when changes are made that should increase theextent of M-C back-bonding, the CO frequencies are shifted toeven lower values. Thus, if some CO groups are replaced byligands with low or negligible back-accepting ability, those COgroups that remain must accept more drc electrons from the metalto prevent the accumulation of negative charge on the metal

"1atom. Hence, the frequency of Cr(CO) is ca. 2000 cm” whereas,6

when three CO's are replaced by amine groups which have essentially no ability to back-accept, as in Cr(CO)3(dien), dien = NH(CH2CH2NH2)2, two CO stretching absorptions are observed at ca. 1900 and ca. 1760 cm"1.

The most important use of infrared spectra of metal carbonyl compounds is in structural diagnosis, whereby bridging and terminal CO groups can be recognised. For terminal M-CO the frequencies of C-0 stretches range 1800-2100 cm"1 but for

42

bridging CO groups the range is 1700-1800 cm 1. These facts may be used to infer structures. In general, we can also state that every unique CO in the molecule will give one stretching frequency while every group of equivalent C O ' s will give two stretching frequencies. In this way we can tell the molecular conformation formed from the number of CO stretching frequencies in the infrared. Symmetry elements can be used to determine the number of infrared active modes. A point group is assigned and symmetry operations performed on the molecule. The active modes can then be determined from character tables.

2.3.2 Infrared S p e c t r o s c o p i c P r o p e r t i e s of Monomer C o m p l e x e s .

The metal carbonyl containing monomers were prepared as described earlier by reaction with photogenerated [M(CO) (THF)]. Metal carbonyl complexes of 2- and 4-

5

vinylpyridine (vp), [M(CO)5(vp)] (M = Cr, Mo, or W), wereobtained as bright yellow crystalline solids and were purified by recrystallisation from degassed ethanol. All the complexes were handled as air sensitive and in general the stability of the complexes is in the order W > Cr >> Mo and 4-vp > 2-vp). The decreased stability of the 2-vinylpyridine may be attributed to

• 2 9steric interaction of the M(CO)g group and the vinyl group The infrared absorption spectra of these complexes show three strong bands due to the C-0 stretch of the carbonyl groups (2100-1700 cm-1) (Table 2.1). The spectra of each pentacarbony1 are identical in all qualitative features (see Fig. 2.1). The pattern and position of the l>cq vibrations are those expected for a M(CO) metal carbonyl moiety and are consistent with a C

43

local symmetry and importantly, the similarity of all the complexes is consistent with bonding of the pyridine through the pyridine ring nitrogen atom68'69. No evidence was found for other complexes such as (rj2-vp)M(CO) , M(CO) (/j-vp)M(CO) , or5 5 b

M(CO) (vp) , indicating that these must be at very best minor4 2

products.

Assignments of the spectral bands can be made from symmetryoperations, and these systems are well characterised and data isavailable for comparison68-71. In Figure 2.1, band 1 is assignedto the A mode. This band occurring ca. 2065-2075 cm-1 is1characteristic of a pentacarbonyl species. Kraihanzel and Cotton70 have assigned band 2 to the mode. This band is Raman active only, but they suggest that it gains some infrared intensity because the structure of the ligand makes it impossible for the molecule to have true C^v symmetry. The T mode of the hexacarbonyls appears around the frequency of the B^ mode also, so the band could be due to hexacarbonyl impurity. Bands 3 and 4 are assigned to the E and A modes respectively,lthe bands being just resolved, the A^ mode appearing as a shoulder.

Reaction of photogenerated [M(CO) (THF)] with5

p-styryldiphenylphosphine (XIV) yields the pentacarbonyl species. The spectral features of the phosphine complex are similar to those of the [M(CO) (vp)] metal carbonyls. However,

56 5Kraihanzel and Cotton stated that in complexes of the type

44

[M(CO) (PPh )], the E and A modes are accidentally degenerate,5 3 1

or so nearly so that the bands are entirely unresolved. Lowering the jr-acceptor strength of the substituent (from phosphine to amine) would lower the frequency of the A mode relative to the E mode and so the bands are resolved in amine complexes. In all spectra of the pentacarbonyl species however, the assignment ofthe E and A modes are difficult due to the broadness of the

1

bands.

Figure 2 shows the spectrum of the tungsten tetracarbonyl complex of 4-vinyl-4'-methyl-2,2'-bipyridyl (XIII) and the frequencies of all compounds are listed in Table 2.1. The four non-degenerate CO stretching frequencies are consistent with a

7 0 7 2 7 3C cis-disubstituted symmetry at the metal centre ' ' . The2 V

assignments of these bands are shown in Figure 2.270. The high frequency band at ca. 2000 cm-1 is indicative of a tetracarbonyl species. The stretching frequencies are close to those previously reported for cis-disubstituted tetracarbonyl 2 , 2 1-bipyridyl complexes72.

45

Table 2.1. The CO stretching frequencies for monomer complexes.

Compì ex yco ( cm"a

*>

W(CO) (4-vp)5 2068 (m) , 1931 (s), 1904 (sh)Cr(CO) (4-vp)O 2063 (m) , 1938 (s), 1907 (sh)Mo(CO) (4-vp)5 2070 (m) , 1944 (s), 1904 (sh)W(C0)s (2-vp) 2067 (m) / 1927 (s) , 1910 (sh)Cr(CO) (2-vp)b 2065 (m) , 1935 (s), 1918 (sh)W(CO) (Vbipy)4 2001 (m) , 1883 (sh) , 1861 (m) , 1808 (s)Cr(CO) (Vbipy)4 2003 (m) , 1890 (s), 1860 (sh), 1807 (s)Mo(CO) (Vbipy)4 2007 (m) , 1887 (s), 1861 (sh), 1810 (s)W(CO) (p-SDPP)5 2069 (m) / 1936 (s)

In N u j o l m u l l s b e t e e n s o d i u m c h l o r i d e w i n d o w s .

v p = v i n y l p y r i d i n e V b i p y = 4 - v i n y l - 4 ' - m e t h y l - 2, 2' - b i p y r i d y l ,

P-SDPP = p a r a - sty r 1 diph e n y 1phosphine .m = m o d e r a t e i n t e n i t y , s = s t r o n g , s h = s h o u l d e r .

46

¿MJ _ ^

w a v e n u m b e r s (cm )

-IH-i■"i--------1------- 1------- 1--------1--------1--------(-------- 1--------T---- T

2260 2000wavenumbers (cm )

Fig.2.1. The CO stretching region of [W(CO) (4-vp)] in nujol. The spectra ofanalogous Cr and Mo complexesare virtually identical.

Band 1: Ai 2068 cm-1Band 3: E 1931 cm-1Band 4: Ai 1904 cm-1

Fig.2.2. The CO stretching region of cis-[W(CO) (Vbipy)]

4in nujol. Cr and Mo complexes have similar spectra.

Band 1: Ai 2001 cm-1 Band 2: Bi 1883 cm-1 Band 3: Ai 1861 cm-1 Band 4: Bz 1807 cm”1

monodentate pentacarbonyl cis-disubstitutedtetracarbony1

/ ¡ \ ^0 O

47

The incorporation of the metal carbonyl fragment into the polymers can be confirmed easily from the strong bands exhibited by the polymer-bound metal carbonyls in the carbonyl stretching frequency region of the infrared spectrum. These bands are well separated from interfering polymer bands. From the number and position of the carbonyl bands the coordination about the metal can be easily determined. The spectra are essentially identical in appearance to those of the analogous monomers. The frequencies of the CO stretching modes are shown in Table 2.2.

2 . 3 . 3 I n f r a r e d S p e c t r o s c o p i c P r o p e r t i e s o f P o l y m e r C o m p l e x e s .

N o t e s on T a b l e 2.2

a All the c o p o l y m e r s w e r e p r e p a r e d so t h a t t h e m o l e r a t i o of m e t a l c a r b o n y l to m o n o m e r was 20/1.

b C h l o r o f o r m f i l m on s o d i u m c h l o r i d e w i n d o w .

C o p o l y m e r s r e p r e s e n t e d thus, P [c o m o n o m e r s ] - M (C O ) , w e r e p r e p a r e dxu s i n g R o u t e 1, w h i l e t h o s e w r i t t e n P [c o m o n o m e r s - M (C O ) ] w e r exp e p a r e d b y R o u t e 2.

P = c o p o l y m e r , E A = e t h y l a c r y l a t e , M A = m e t h y l a c r y l a t e

M M A = m e t h y l m e t h a c r y 1 ate

v p = v i n y 1p y r i d i n e , p - S D P P = p - s t y r 1 d i p h e n y 1p h o s p h i n e

V b i p y = 4 - v i n y 1 - 4 ' - m e t h y 1 - 2 , 2 ' - b i p y r i d y 1.*P e n t a c a r b o n y 1 a n d t e t r a c a r b o n y 1 s p e c i e s b o t h p r e s e n t .

- 1P e a k a s s i g n m e n t s a r e a c c u r a t e to +/- 3 c m

w = w e a k i n t e n s i t y , m = m o d e r a t e , s = s t r o n g , sh = s h o u l d e r .

t B a n d s d u e to C = 0 s t r e t c h of a c r y l a t e p o l y m e r b a c k b o n e .

48

Table 2.2. Infrared Spectral Data in the Carbonyl Stretching Region for Polymer Complexes.

Complex3 v (cm-1)bCO

P[styrene-W(CO) (4-vp)]5 20 68(m), 1926(s ), 1892(sh)P[styrene-Cr(CO) (4-vp)] 20 64(m), 1929(s), 1900(sh)P[styrene-Mo(CO) (4-vp)] 2070(m), 1935(s ), 1905(sh)P[styrene-(4-vp)]W(CO)s 2068(m), 192 6(s ), 1890(sh)P[styrene-(4-vp)]Cr(CO) 2064(m), 1929(s ), 1900(sh)P[styrene-(4-vp)]Mo(CO) 2070(m), 1935(s), 1900(sh)*P[styrene-(Vbipy)]W(CO) 4 2072(w), 2002(m), 1931(s ), 1881(s )

1865(sh) , 1825(s )P[styrene-W(CO) (Vbipy)]4 2003(m), 18 90(s ) , 1876(sh), 1830(s)*P[styrene-(Vbipy)]Cr(CO) 4 2070(vw) , 2003(m) , 1930(w ) , 1892(s )

1870(sh) , 182 6(s )P[styrene-Cr(CO) (Vbipy)]4 2001(m), 1890(s), 187 8(sh), 1830(s )P[styrene-(Vbipy)]Mo(CO) 4 2008(m), 1898(s ), 187 6(sh), 1831(s )P [EA-W(CO) (4-vp)]5 2069(m), 1926(s ), 1890(sh),+1724(s)P[EA-Cr(CO)5(4-vp)] 20 65(m), 1934(s ), 1898(sh),+1727(s)P [EA-W(CO) (Vbipy)]4 2001(m), 1883(s ) , 1858(sh), 1830(m)

+1726(s)P[MA-W(CO)5(4-vp)] 2069(s), 1914(s ) , 1885(sh),+1727(s)P[MMA-W(CO) (4-vp)]5 2068(m), 1933(s ) , 1900(sh),+17 23(s )P[MMA-Cr(CO) (4-vp)] 20 65(m), 1935(s ) , 1895(sh),+1723(s)P[MMA-Mo(CO) (4-vp)]5 2071(m), 1936(s) , 1898(sh),+1723(s)*P[styrene-(p-SDPP)]W(CO) 20 68(m), 2012(m), 1935(s ), 1888(sh)*P[styrene-(p-SDPP)]Cr(CO) 2069(m), 2004(m), 1936(s), 1883(sh)*P[styrene-(p-SDPP)]Mo(CO) 5 2069(m), 2017(m), 1942(s), 1903(sh)P [styrene-W(CO) (p-SDPP)] 207 2(m), 1935(s ), 1910(sh)P[(4-vp)-W(CO)g(4-vp)] 2069(w), 1924(s), 1895(sh)P[(2-vp)-W(CO) (2-vp)]b 2069(w), 1931(s ), 1905(sh)

4 9

!

2 2 0 0 2 0 0 9 1 7 0 0

wavenumbers (cm”1)

Fig. 2.3. The CO stretching frequency region of a copolymer of styrene and [W(CO)g(4-vp)].The spectra of the Cr and Mo copolymers are very similar.

_ jwavenumbers (cm” ^Fig. 2.4. The CO stretching frequency region of a copolymer of styrene and Vbipy which when reacted with [W(CO) (THF)], produced a

5species containing both bound cis-tetracarbonyl moieties and pentacarbonyl moieties.

50

to those of their monomeric analogues indicating that thesymmetry at the metal centre is unchanged upon polymer-binding. Comparing both methods of synthesising the polymer-bound metal carbonyls, preformed copolymers of styrene and vinylpyridine to which the metal carbonyl fragment was reacted (Route 1) exhibit similar bands to those of a copolymer of styrene and[W(CO) (vp)] (vp = 2- or 4- vinylpyridine) (Route 2). The band

5

at ca. 2068 cm-1 is the characteristic high energy pentacarbonyl band. However, preformed copolymers of styrene and 4-vinyl-4'-methyl-2,2'-bipyridyl which were reacted with [M(CO) (THF)] (M = Cr or W) have CO stretching bands assignable

5

to both the expected cis-tetracarbonyl species (A : 2002,lB : 1881, A : 1865 and B : 1825 cm"1) and the pentacarbonyl1 1 2species (A : 2072, E: 1931 cm-1) (Figure 2.3). This observationlwas of interest as the isolation of monodentate monomeric a-diimine ligands has proven difficult, because the chelation reactions of these complexes occur on fast timescales, and as a result, flash photolysis techniques must be used for their study640. In one study, Oshi investigated the flash photolysisof Cr(CO) in the presence of phenanthroline, and concluded that

6

the rate of formation of [Cr(CO) (phenanthroline)] depended on5

the substituents on phenanthroline64d. In addition studies have shown that 2,21-bipyridyl exists in solution in an s-trans conformation. Such a conformation would require rotation about the C-C bond to form the bidentate product. The presence of the polymer chain may hinder the formation of the tetracarbony1

The number and position of the bands are almost identical

51

species by restricting rotation of the bound bipyridyl. No evidence for the [(M(CO) ) (bipy)] was found. Those copolymers

5 2

of styrene and [M(CO) (Vbipy)] show bands only due to the metal4

tetracarbonyl species.

Disubstituted derivatives were also formed on reaction of [W(CO)g(THF)] with copolymers of styrene andp-styryldiphenylphosphine. Bands arising form thecis-disubstituted metal carbonyl species were observed, as well

65 \ 6as the expected pentacarbonyl bands . Pittman , in his study of group 6 metal carbonyls attached to polymers containing phosphine units, found similar spectroscopic evidence for the formation of the trans-disubstituted derivative. He stated that this observation attested to the high degree of mobility of the coordination sites within these matrices. Collman and coworkers74 earlier emphasised this mobility and general tendency toward chelation in the reactions of resin-substituted triphenylphosphine with [IrCl(CO)(PPh^)^] and [RhC1(CO)(PPh3)2] •

52

Considerable effort has been directed toward understanding the electronic structure of carbonyl complexes of Cr, Mo, and W. The band position, intensity, and likely assignments for the electronic transitions of a large number of metal carbonyls and their derivatives have been determined, and many of the results have proved valuable in a number of photochemical systems. Generally, the complexes exhibit a number of intense (e >10 ) transitions in the UV-visible region which are associated withligand field (LF) and M ---► L and L ---> M charge-transfer (CT)absorptions17'25' 32 .

The UV spectra of M(CO) (M = Cr, Mo, or W) compounds are6

dominated by two intense (e >104) metal-to-1igand chargetransfer (M ---> LCT) bands at ca. 280 nm and ca. 230 nm. Alsoseen as shoulders on these large peaks are two strong (e >10 ) ligand field (LF) transitions at c a . 3 2 0 nm and ca. 260 nm assigned as 1A ---> aT and 1A ---> 1T , respectively. Eachlg lg lg 2 g

observed LF transition weakens both the n and a components ofthe M-CO bond making M(CO) (and metal carbonyls in general)

6

among the most photoreactive metal complexes known. The dominantphotoreaction for M(CO) , therefore, is dissociation of CO.

6

In absorption spectra for C [M(CO) L] (L << CO in ligand4 v 5

field strength), the lowest energy absorption corresponds to aligand field 1A (e4b2) » 1E(e3bza1) transition around 400 nm,1 2 2 1

for ligands L having no low-lying it levels (e.g. piperidine)69

2 . 3 . 4 U V / V i s i b l e S p e c t r o s c o p i c P r o p e r t i e s o f Me t a l C a r b o n y l s .

53

M( CO ) transition. For M = W the spin-forbidden61A (e4b2) ---> 3E(e3b2a1) transition has significant intensity.1 2 2 1

*If the ligand L has low lying n orbitals, a MLCT absorption can be the lowest energy transition. When L = 4-formylpyridine the complex has a low-lying MLCT absorption, while exhibiting all of the low-lying LF bands present when L = piperidine. Variation in the pyridine substituents results in variation in the CT band position69. The more electron-releasing substituents give a higher energy CT. MLCT bands are very sensitive to solvent polarity; more polar solvents give blue-shifted CT band maxima, while LF bands are little affected. Consequently, when LF and MLCT bands are overlapping, it is possible to resolve them by varying the polarity of the solvent.

The electronic spectra of C^v disubstituted complexes cis-[M(CO) L ] or [M(CO) (L-L)] are basically similar to the4 2 4

monosubstituted complexes. For a-donor only ligands the lowest transition is a ligand field transition ( A ---> A B ) around

1 l g 2

420 nm (slightly lower than for [M(CO) L]). If the ligand can5

function as a ji-acceptor, MLCT and intraligand transitions are often observed as the lowest energy transitions. Among metal carbonyls, the only mononuclear complexes which have been investigated which unequivocally have a MLCT lowest excited state are [M(CO) L]64'75. For these complexes the M > LCT4

transition yielded no detectable CO substitution.

(see Figure 2.6). This is at lower energy than the corresponding

54

2 g

dz2

d 2 2x - y

e — • — d dxz yzb --- d

2 xy

■ V

V - y 2

— — d , d , dxz yz xy

M(CO) M(CO) L s M(CO) LV ' 4 2

'4v ' 2v

Fig. 2.6 The one electron diagram for 0^, and complexes.

2.3.5 U V / V i s i b l e S p e c t r o s c o p i c P r o p e r t i e s o f P o l y m e r Systems

A comparison of the UV/vis spectra (270-500 nm) of a copolymer of styrene and 4-vinylpyridine and the tungsten carbonyl analogue in chloroform solution is shown in Figure 2.7. Low-lying LF transitions and MLCT are observed. The electronic spectrum and position of the bands are very similar to those of [W(CO) (pyridine)] in the region 300-500 nm (see Figure 2.8).5

Three distinct transitions can be observed. Each [W(CO) (4-vp)] polymer exhibits a low energy band near 440 nm,5

17 6 9 71 7*5which is the one previously associated ' ' ' with thespin-forbidden LF 1A (e4b2) -- » 3E(e3b2a1) transition. The1 2 2 1corresponding singlet-singlet LF transition is associated with

55

and poly[styrene-W(CO) (4-vp)] (--- ) in chloroform solution.5

Fig. 2.7. UV/Visible spectrum of poly[styrene-(4-vp)] (------ )

Fig.2.8. Comparison of the UV/vis spectra of [W(CO) (py)] (----)5

and P[styrene-W(CO).(4-vp)] (--- ) in chloroform solution.

56

the absorption band near 380 nm. The band at around 340 nm has been assigned to a MLCT band in [W(CO) (Xpy)] complexes where

5

Xpy is pyridine or a substituted pyridine. The position of the MLCT band is very sensitive to the solvent, while LF bands are unaffected by solvent polarity. The effect of the solvent on the electronic absorption spectrum of a copolymer of styrene and [W(CO) (4-vp)] was investigated (although the solvent polarity

5

range is severely restricted due to the insolubility of the polymer in many non-polar and polar solvents). A marked solvent dependence was found for the X of the band at around 335 nm.m a x

This absorption band can then be assigned to a W ---► LCTtransition of the polymer-bound [W(CO) (py-CH-CH-)] group. While

5 2

the MLCT band blue shifts as the solvent polarity increases, the LF transitions at around 376 and 440 nm remain relatively unaffected. The affect of solvent is shown in Table 2.4 and illustrated in Figure 2.9.

Figure 2.9 Effect of solvent on the MLCT band of polymer-bound [W(CO) (py-CH-CH-)].

b Z

57

Table 2.4 Spectral Band Maxima and Assignments for polymer-bound [W(CO)s(py-CH-CH—)].

Solvent 1A ( e4b2 ) ---»1 23E(e3b2a 1)2 1

nm

*A ( e4b 2 ) --->1 23E(e3b 2a 1) v 2 1

nmW ---» LCT

nm

DMF 438 378 318Dichloromethane 440 374 330Benzene 440 375 335Tetrahydrofuran 442 378 332Chioroform 442 376 334Toluene 442 375 338ccl

4436 380 342

Absorption spectra of a copolymer of styrene and [W(CO) (4-vinyl-41-methyl-2,2'-bipyridyl)] were recorded in a

4

number of solvents. A spectrum of the copolymer is shown in Figure 2.10. The spectrum shows two well resolved bands in the region 320-500 nm in contrast to those spectra of [M(CO) (4-vp)], where considerable overlap of LF and MLCT bands

5

occurs in copolymers of [M(C0)5(4-vp)]. In the case of M = Cr or Mo the MLCT bands cannot be distinguished. The broad and intense long wavelength absorption band near 500 nm has been assigned to a lowest energy MLCT absorption in complexes of the type [M(CO) (L)], where L denotes a bidentate diimine such as

4■ ■ 7 7 7 02,2'-bipyridyl ' . The impressive solvochromatic behaviour of

these complexes with solvent-dependent shifts of the low energy band gives additional support for the MLCT assignment. Table 2.5

58

shows the effect of solvent polarity on the tetracarbony1

copolymer.

Figure 2.10 Absorption spectrum of a copolymer of styrene and [W(CO) (4-vinyl-4'-methyl-2,2'-bipyridyl)] in CH Cl .

4

Table 2.5 Band Maxima and Assignments for a Copolymer of Styrene and [W(CO) (4-vinyl-4'-methyl-2,2'-bipyridyl)] in a variety of

4solvents.

Solvent LF (aA ---» *A 1B )i ig 2

nmW ---» LCT

nmDMF 385 445Diehloromethane 376 470Benzene 380 477Tetrahydrofuran 377 485Chioroform 376 492Toluene 373 500

5 9

The band centered around 490 nm (CHCl3 solution) shows marked solvent dependence. On the basis of previously published work on complexes of the type cis-[W(C0) (bipy)], this band can

4

be assigned to a MLCT transition, as the absorption blue shifts in progressively more polar solvent media. The LF band at around 380 nm is relatively unaffected. There has been much interest in metal carbonyls of the type [M(C0) (L)], where L is

4

2,2'-bipyridine, because their low-lying MLCT states are so well resolved from higher LF states that they offer an opportunity to study the photophysical and photochemical properties of the MLCT excited states exclusively77.

In [W(CO) (Xpy)] complexes, where Xpy is a substituted5

pyridine, the MLCT band was found to depend on the electronic nature of the substituent X69. The position of the MLCT can be changed rather dramatically by tampering with the electronic nature of the substituent X. As the pyridine substituent becomes more electron withdrawing, the MLCT transition shifts to longer wavelength. The position of the MLCT band in copolymers of [M(CO) (4-vp)] is also sensitive to the composition of the

5

polymer backbone. (Table 2.6 gives some data for copolymers in chloroform solution). It should be noted that for the styrene-4-vinylpyridine-[M(CO) (4-vp)] terpolymers the position

5

of the MLCT band shifts to longer wavelength as the proportion of vinylpyridine in the copolymer is increased. Surprisingly the shift is in the direction expected for an increasingly less-polar environment of the bound [W(CO) (py-CH-CH-)].

5 2

60

Presumably the environment of the complex is determined both by the solvent and by the presence of the other polymer chains, the extent of each being controlled by the tightness of the polymer coil in the solvent29. The position of the MLCT bands in these polymer systems are sensitive to both solvent and polymer backbone composition. These observations confirm the view that it should be possible to "tune" the photochemical properties of organometal1ic compounds by binding them to polymers and hopefully it may be possible in this way to develop more effective photocatalysts.

Table 2.6 Variation with Polymer Backbone Composition of the Absorption bands of [W(CO)g(4-vp)] copolymers in chloroform soluti on.

Backbone3 LF (1A1-- >3E)nm

LF (1A 1-- S e )

nmMLCTnm

Styrene 442 376 336Styrene/4-vp (5/1) 438 376 3384-vp 440 375 344Methyl acrylate 438 378 342Methylmethacrylate 438 378 346Ethyl acrylate 440 380 340a-methyl styrene 440 376 348

a A l l the c o p o l y m e r s w e r e p r e p a r e d u s i n g a 2 0 / 1 m o l e r a t i oof m o n o m e r to [W(CO) (4-vp)] u n l e s s i n d i c a t e d o t h e r w i s e .5

61

Figure 2.11 The Variation of the Absorption Bands of Copolymers of [W(CO) (4^vp)] in Chloroform Solution.

5

6 2

2 . 3 . 6 G e l Permeation Chromatography (GPC).Gel permeation chromatography76 is a widely used technique

employed in the characterisation of polymer materials. The separation in GPC is based on molecular size, the molecule being restricted by it's ability (depending on it's size) to penetrate the pore structure of the gel separation media. In molecular weight determinations, calibration curves are prepared by running polystyrene standards of known molecular weight, and preparing a plot of log molecular weight versus retention volume. This plot is usually linear over a wide range of molecular weights. However, the true nature of the separation in GPC is based on hydrodynamic volume and not molecular weight. So, a calibration made with narrow distribution linear polystyrene will not apply to a polymer of another composition. The availability of narrow distribution polymers is restricted to only a few polymers and so standards are not available to give a true indication of the molecular weight. An approximate correction (Q-factor) is often applied which takes into account the differences in molecular weight per unit chain length. However, in this instance comparisons between various samples only is required so the use of a calibration curve is adequate.

GPC has been previously used to characterise polymer-bound metal carbonyls. Pittman characterised polystyrene polymers to which he attached M(CO) moieties52. GPC showed that the narrow

3

molecular distribution of the polystyrene was maintained following complexation to the phenyl residues, and that no decomposition of the polymer occurred during reaction. He found

6 3

an increase in the number average molecular weight (wn ) on anchoring of the metal tricarbonyl. He used the Mn to calculate the percentage complexation and results agreed well with elemental analyses. In another study, Pittman used GPC to fractionate a wide molecular weight distribution formed on the bulk homopolymérisation of (r)5-viny 1 cyclopentadienyl )-dicarbonylnitrosylchromium (see VIII section 1). From these fractions a GPC calibration curve was constructed for a polymer of VIII.

In this work, molecular weight studies were performed by gel permeation chromatography in THF. A calibration curve was constructed using narrow distribution polystyrene standards. Several styrene copolymers were examined and shown to be true polymers of a relatively narrow molecular weight distribution in each case. On attaching the metal carbonyl complexes to these copolymers, GPC data demonstrated that the narrow molecular weight distribution was maintained (see Figure 2.12). No low molecular weight polymer was observed, indicating that the copolymers did not degrade during reaction. Similar copolymers prepared by the polymerisation of styrene with the metal carbonyl monomer produced polymers of comparable distributions. The data is shown in Table 2.4.

64

Poly[styrene-(4-vp)]W(CO) (... ) in THF.5

Figure 2.12 GPC chromatogram of Poly[styrene-(4 - v p )] (---- ) and

Table 2.7. GPC Molecular Weight Determinations for a Representative Series of Copolymers.

Polymer3 Mn Mw M / M w n

P[styrene-(4-vp)] 8180 17200 2 .11P[styrene-(4-vp)]W(C0)

510100 27500 2.72

P[styrene-(Vbipy)] 14900 36800 2.46P [styrene-(Vbipy)]W(C0)

420200 58100 2 . 87

P[styrene-W(CO) (4-vp)]5

12870 39150 3.04

E a c h c o p o l y m e r w a s p r e p a r e d so t h a t t h e m o l e r a t i o of m e t a l c a r b o n y l t o m o n o m e r w a s 1 / 2 0

Mn = number average molecular weight (a.m.u).M = weight average molecular weight (a.m.u). w

65

2.3.7 Determination of M e t a l I n c o r p o r a t i o n .

Atomic absorption spectroscopy was used to determine the extent of metal incorporation in the polymer-bound materials. The data for different polymer types is presented in Table 2.5. In general, a high percentage of metal was incorporated onto the polymers, but the important thing to note is the difference in percentage metal incorporation found on comparing the two methods of syntheses. Those polymers prepared via the copolymerisation of the functionalised monomer containing the metal carbonyl and comonomer (Route 2) contained a higher percentage metal than those preformed copolymers which were then reacted with the [M(CO)s(THF)] (M = Cr, Mo, or W) species.

Table 2.8. Metal Analyses of Polymer-Bound Metal Carbonyls.

Polymer % Metal IncorporationTheory Found

P[styrene-(4-vp)]W(CO)s 7 . 32 5.42P[styrene-W(CO) (4-vp)] 7 . 32 6.35P[styrene-(Vbipy)]W(CO)

47 .14 5.28

P[styrene-W(CO) (Vbipy)]4

7 .14 6.07P[styrene-(4-vp)]Cr(CO) 2.19 1. 69P[styrene-Cr(CO) (4-vp)]5 2.19 1. 91P[styrene-(4-vp)]Mo(CO)s 3 . 96 2.49P [styrene-Mo(CO)g(4-vp)] 3.96 3.27P[styrene-(2-vp)]W(CO) 5 7.32 5.41P[styrene-W(CO) (2-vp)] 7 . 32 6 .2 2P [MA-W(CO) (4-vp)] 8 . 55 7 . 29P[(4-vp)-W(CO)s (4-vp)] 7 .26 6 .1 2P[styrene-W(CO) (p-SDPP)] 6.82 5.79P [styrene-(p-SDPP)]W(CO) 6.82 4. 64P[styrene-(p-SDPP)]Cr(CO)5 2.03 1.50P[styrene-(p-SDPP)]Mo(CO)

53. 68 2.28

6 6

2.4. Investigation of the Interaction of Metal Carbony1s withPolymeric Supports.

The reaction of the metal carbonyl fragments with polymeric supports was studied using laser flash photolysis. In effect we were investigating the synthesis routes used in the preparation of these polymer-bound materials. The first method of synthesising these polymer materials discussed involved the formation of the solvent adduct and it's subsequent reaction with the polymer backbone containing pendant sites (Route 1). Laser flash photolysis allows us to detect the short-lived primary photoproduct, M(CO)gS (S = solvent), and to determine it's rate of reaction with the polymer support. The observationof an intermediate following the photolysis of M(CO) in toluene

6

solvent at room temperature is reported and the kinetics of it's subsequent reactions with monomeric pyridine and polymer-bound pyridine are determined. Toluene was chosen because it is a goodsolvent for copolymers of styrene and 4-vinylpyridine, andbecause of the insolubility of the copolymers in many of the popularly used solvents. In addition, little work in this area using toluene has been reported. However, the choice of toluene as the solvent causes experimental problems. Because toluene absorbs below 290 nm it restricts the region of the spectrum we can investigate, and the laser frequency we can use(X = 355 nm) . The flash photolysis experiment is one of monitoring absorbance changes, following pulsed-laserphotolysis. The experimental procedures and laser equipment are discussed in greater detail in section 5.

67

Following initial studies by Strohmeier and coworkers24 the photochemical behaviour of group 6 metal carbonyls have been the subject of numerous investigations. Intermediates produced in the photolysis of group 6 hexacarbonyls have been studied in 1ow-temperature glasses and matrices, in the liquid phase, and

• 1 7 2 4 2 5in the gas phase, and have been widely reviewed . In morerecent studies, conventional flash photolysis techniques have provided information about intermediates produced in these

7 3 0 4photolyses " . The primary photoreaction in solution is one ofefficient CO dissociation to form the coordinatively unsaturated pentacarbonyl species. This highly reactive species coordinates to the solvent to produce an observable M(CO)gS intermediate. In the presence of coordinating ligand L, the substitution product M(CO) L is formed with near unitary quantum efficiency.

5

M (CO ) + hy > M(CO) + CO6 5

M (CO ) + S > M(CO) S5 ' ' 5

M (CO) S + L ------ » M(CO) L + S5 5

It is the structure, the solvation, and the reaction kinetics of the M(CO)s species that has been of much interest. Extensive studies in 1ow-temperature matrices supported the presence of an intermediate with a C square-pyramidal structure and one which

4 V

could undergo thermal reaction with the photoproduced or added0 5 0 6CO ' . Direct comparison with visible absorption bands of

matrix-isolated M(CO) is difficult because of wavelength shifts5

produced by M(CO) matrix interactions. M(CO) interacts with5 5

2 . 4 . 1 Photochemistry of Group 6 Me t a l C a r b o n y l s .

68

solvent molecules and in solution the M(CO) species cannot be5

considered as "naked". These highly reactive coordinativelyunsaturated species have been shown to react with materials which would normally be considered inert, such as dinitrogen84 and alkanes86, and their formation and reactions in the liquidphase has been reported to be very fast. Simon and Xie84reported a rise time of less than 0.8 ps for the formation of Cr(CO) (cyclohexane) in cyclohexane solution.

2 . 4 . 2 Laser F l a s h P h o t o l y s i s w i t h U V / v i s M o n i t o r i n g

Using laser flash photolysis techniques intermediates can be detected on a timescale comparable to the fastest chemical processes in solution, and the technique provides information about primary photochemical processes in organometal1ic compounds. Detection of short lived primary photoproducts and the determination of the rates of coordination, and especially the influence of the solvent on these rates is of particularinterest.

In principle, flash photolysis involves the generation of a high concentration of a short-lived intermediate using a high intensity pulse of radiation of very short duration. At a short time interval after the generating pulse the system is analysed by observing the intermediates emission or absorption characteristics. The process can be followed by photographing the emission spectrum using a spectrograph, or the absorption spectrum can be measured by triggering an analytical beam

69

passing through the reaction cell to flash at a predetermined time interval after the initial flash. Alternatively, the process may be followed kinetically by monitoring the emission or absorption at a particular wavelength using a detector coupled to an oscilloscope with a time-based sweep. The polychromatic nature of the radiation from conventional discharge tubes increases the possibility of generating more than one emitting or absorbing species. Lasers overcome this problem because their radiation is monochromatic. Other advantages of lasers are that the pulse is of very short duration (Q-switching) and highly reproducible. Frequency doubling and mixing can be used to increase the range of the laser source from it's fundamental harmonic. Oscilloscope traces of the transient are recorded using a high intensity monitoring beam which helps to overcome problems caused by background noise with lower intensity sources. UV/vis spectra of the transient are obtained point by point by changing the monitoring wavelength on the monochromator and recording a series of readings at a fixed time interval after the flash.

70

2 . 4 . 3 Laser Flash P h o t o l y s i s S t u d i e s of Vf(CO)^ Toluene S o l u t i o n s

C o n t a i n i n g a Polymer-Bound P y r i d i n e L i g a n d .

The aim of this study was to compare the reaction kineticsof intermediates produced in the photolysis of W(CO) in toluene

6

solutions containing a poly(styrene-co-4-vinylpyridine) copolymer of various compositions with those of monomeric pyridine.

Laser pulse photolysis at 355 nm of W(CO) in room6

temperature toluene produces an intermediate proposed to beW(CO)5(toluene), with an absorption maximum at 415 nm (seeFigure 2.4.3). The position of the maximum is within the rangeof wavelengths reported for tungsten pentacarbonyl speciesgenerated in 1ow-temperature matrices [SF (461 nm),6Ar (437 nm), Xe (417 nm) , and CH (413 nm)]85. In the presence

4

of added pyridine (monomeric or polymeric) the intermediatereacts to form W(CO) (pyridine), having a absorption maximum at

5

around 390 nm.

W(CO)g + toluene — STSTnm * w (C°)5(toluene) + COk

W(CO) (toluene) + L --- ----- > W(CO) L + toluene5 5

The W(CO) (pyridine) species is stable and it's UV/vis5

absorption spectrum exhibits bands at around 395 and 440 nm attributable to LF transitions of W(CO) (pyridine) previously

563reported . Typical transients obtained are shown in

Figures 2.4.1 and 2.4.2. The oscilloscope is set with a delay to

71

e n a b l e t h e i n i t i a l a b s o r b a n c e t o b e r e c o r d e d , a n d t h e t r a c e

s ho ws t h e r a t e o f c h a n g e i n a b s o r b a n c e o f t h e t r a n s i e n t s p e c i e s

w i t h t i m e . A l l r e a c t i o n s w e r e f o u n d t o f o l l o w f i r s t o r d e r

k i n e t i c s . The t r a c e s w e r e a n a l y s e d k i n e t i c a l l y t o d e t e r m i n e t h e

o b s e r v e d r a t e c o n s t a n t s f o r t h e r e a c t i o n s . The W(CO) ( t o l u e n e )5

s p e c i e s i s f o r m e d i m m e d i a t e l y i n t h e f l a s h a n d i t ' s f o r m a t i o n i s

t o o r a p i d t o b e d e t e c t e d w i t h t h e e q u i p m e n t a v a i l a b l e .

F i g u r e 2 . 4 . 1 s ho ws t h e f o r m a t i o n o f t h e i n t e r m e d i a t e i n t h e

l a s e r p u l s e a t 310 nm, f o l l o w e d by i t ' s d e c a y a s i t r e a c t s w i t h

t h e a d d e d l i g a n d . The f o r m a t i o n o f W(CO)s L i s s hown i n

F i g u r e 2 . 4 . 2 a t 390 nm. The W(CO) ( t o l u e n e ) i s f o r m e d i n t h e5

p u l s e a s b e f o r e a n d t h e l i g a n d s p e c i e s " g r o w s - i n " a t a r a t e

e q u a l t o t h e r a t e o f d e c a y o f t h e W(CO) ( t o l u e n e ) s p e c i e s . A5

t r a n s i e n t a b s o r p t i o n d i f f e r e n c e s p e c t r u m i s s ho wn i n

F i g u r e 2 . 4 . 3 . A b s o r b a n c e r e a d i n g s w e r e r e c o r d e d a t d i f f e r e n t

m o n i t o r i n g w a v e l e n g t h s i m m e d i a t e l y a f t e r t h e l a s e r p u l s e a n d

a f t e r t h e d e c a y o f t h e t r a n s i e n t .

72

Fig. 2.4.1photolysis of W(CO)

T r a n s i e n t d a t a r e c o r d e d a t (1 X1 0_7M) a n d 2 X 1 0 ' 2M

c o p o l y m e r o f s t y r e n e a n d( T i m e b a s e = 2 0 0 / j s / c h a n n e l ; k = 7 8 . 2 2ob s

310 nmp y r i d i n e

4 - v i n y l p y r i d i n e i n - 1 ■)

f o i l o w i ng

i n a 5 / 1 t o l u e n e .

«

time

F i g . 2 . 2 . 2 T r a n s i e n t d a t a r e c o r d e d

p h o t o l y s i s o f W(CO) ( 1X 10 "7M) a n d 2X10"ZM6

c o p o l y m e r o f s t y r e n e a n d( T i m e b a s e = 2 0 0 f i s / c h a n n e l ; k = 6 9 . 0 1 sob 8

a t 3 90 nm

p y r i d i n e

4 - v i n y l p y r i d i n e i n- l ) .

f o i l o w i n g

i n a 5 / 1

t o l u e n e .

time

73

F i g . 2 . 4 . 3 T r a n s i e n t U V / v i s d i f f e r e n c e s p e c t r u m r e c o r d e d

i m m e d i a t e l y a f t e r l a s e r p u l s e a n d a f t e r d e c a y o f t r a n s i e n t .

Absorbance (X10E-2)

wavelength (nm)

The r a t e o f d i s a p p e a r a n c e o f t h e i n t e r m e d i a t e f o l l o w s

p s e u d o f i r s t o r d e r k i n e t i c s . A p l o t o f k v e r s u s p y r i d i n eob sc o n c e n t r a t i o n g i v e s t h e s e c o n d o r d e r r a t e c o n s t a n t , a s t h e

s l o p e .

kW(CO) ( t o l u e n e ) + L ----------- > W(CO) L + t o l u e n e

5 5

To d e t e r m i n e t h e e f f e c t o f t h e p o l y m e r b a c k b o n e , t h e k o f

m o n o m e r i c p y r i d i n e i n t o l u e n e s o l u t i o n was c o m p a r e d t o t h a t o f

t h e k o b t a i n e d f o r t h e s ame c o n c e n t r a t i o n o f p y r i d i n e i n2

c o p o l y m e r s o f d i f f e r e n t l o a d i n g o f s t y r e n e t o 4 - v i n y l p y r i d i n e

( l o a d i n g d e t e r m i n e d by % N m i c r o a n a l y s i s ) . The v a r i a t i o n o f k obsw i t h p y r i d i n e c o n c e n t r a t i o n i s s hown i n F i g u r e 2 . 4 . 4 , a n d t h e

v a l u e s o f k a r e g i v e n i n T a b l e 2 . 4 . 1 .2

74

F i g . 2 . 4 . 4 P l o t o f k v e r s u s [ p y r i d i n e ] .ob 8

Koba (/s)

[py] (X10E-2)

10/1 Loading — 5/ 1 Loading - b - Pyrid ine

T a b l e 2 . 4 . 1 S e c o n d o r d e r r a t e c o n s t a n t s .

S a m p l e k 2 (dm3mol a s *)

P y r i d i n e 0 . 9 X 1 0 3

5 / l a C o p o l y m e r 3 . 2 X 1 0 3

1 0 / 1 C o p o l y m e r 1 . 4 X 1 0 3

Refers to the mole ratio of styrene to 4 - v i n yl p yr i di n e .

75

S u r p r i s i n g l y , t h e s e c o n d o r d e r r a t e c o n s t a n t s f o r t h e

c o p o l y m e r s a r e h i g h e r t h a n t h o s e f o r f r e e p y r i d i n e i n t o l u e n e

s o l u t i o n . One may h a v e e x p e c t e d a d i f f e r e n c e i n s e c o n d o r d e r

r a t e s b e c a u s e p e r h a p s o f d i f f u s i o n c o n s t r a i n t s p o s e d by t h e

p o l y m e r c o i l s i n s o l u t i o n , b u t t h e n we w o u l d e x p e c t k t o b e

h i g h e r f o r m o n o m e r i c p y r i d i n e . The c o p o l y m e r s h a v e d i f f e r e n t k 2v a l u e s f r o m o n e a n o t h e r , t h e h i g h e r l o a d i n g ( 5 / 1 ) p o l y m e r h a v i n g

t h e h i g h e r r a t e c o n s t a n t . The e f f e c t c o u l d p e r h a p s b e

t h e r m o d y n a m i c i n o r i g i n . T h e d i f f e r e n c e i n r a t e s c o u l d b e

a t t r i b u t a b l e t o a d i f f e r e n c e i n t h e s p o n t a n e i t y o f t h e

r e a c t i o n s , i . e . , a d i f f e r e n c e i n t h e f r e e e n e r g y c h a n g e o f. . j*a c t i v a t i o n , AG+ .

The a c t i v a t i o n p a r a m e t e r s w e r e c a l c u l a t e d f r o m t h e

A r r h e n i u s a n d E y r i n g e q u a t i o n s 0 7 . The A r r h e n i u s e q u a t i o n i s

g i v e n by :

I n k = I n A - E^ ( 1 )aRT

w h e r e A i s t h e f r e q u e n c y f a c t o r , a n d E^ i s t h e a c t i v a t i o n e n e r g y

o f t h e a c t i v a t e d c o m p l e x . The r a t e c o n s t a n t i s d e p e n d e n t on t h e

e n e r g y o f a c t i v a t i o n . A p l o t o f I n k v e r s u s 1 / T s h o u l d g i v e aob ss t r a i g h t l i n e o f s l o p e o f - E ^ / R . F r om t r a n s i t i o n - s t a t e t h e o r y i nGL

t h e r m o d y n a m i c s we o b t a i n t h e E y r i n g e q u a t i o n :

k = kT ( 2 )2 T

76

s o t h a t k a AG * a n d i f AG* = AH* - TAS* t h e n2

k2

k T ( a i S * / R . e - A H * / R T ) ( 3 )

w h e r e AG*, AH*, a n d AS* a r e c a l l e d t h e G i b b s f r e e e n e r g y c h a n g e

o f a c t i v a t i o n , t h e e n t h a l p y c h a n g e o f a c t i v a t i o n , a n d t h e

e n t r o p y c h a n g e o f a c t i v a t i o n ( k i s t h e B o l t z m a n n c o n s t a n t a n d h

t h e P l a n c k c o n s t a n t ) . I t f o l l o w s f r o m ( 3 ) t h e n t h a t :

The s a m p l e s c o n t a i n i n g t h e h e x a c a r b o n y l (1X10" M) a n d

a n d t h e t r a n s i e n t r e c o r d e d a t a m o n i t o r i n g w a v e l e n g t h o f 395 nm.

The o b s e r v e d r a t e c o n s t a n t s w e r e c a l c u l a t e d a t e a c h t e m p e r a t u r e .

The e x p e r i m e n t a l r e s u l t s a r e t a b u l a t e d i n T a b l e s 2 . 4 . 3 t o 2 . 4 . 5 ,

a n d c o r r e s p o n d i n g p l o t s shown i n F i g u r e s 2 . 4 . 5 t o 2 . 4 . 1 0 . The

a c t i v a t i o n p a r a m e t e r s a r e s hown i n T a b l e 2 . 4 . 2 .

I n k + AS* + H T R~

-AH* 1 ( 4 ) RT

I n kT

From a p l o t o f l n (k / T ) versus 1 / T we c a n f i n d AH* a n d AS*.

Si o peR

a n d I n t e r c e p t I n k + AS* ~ T T R"

2X10"2M p y r i d i n e i n t o l u e n e w e r e h e a t e d i n i n c r e m e n t s o f 5 K

77

W(CO) ( p y r i d i n e ) on f l a s h p h o t o l y s i s o f W(CO) i n t o l u e n e i n t h e 5 6p r e s e n c e o f a p y r i d i n e l i g a n d .

Table 2.4.2 Activation parameters for the formation of

S a m p l eE*a

( K J m o l " 1)

AH*

( K J m o l - 1 )

AS*

( J K ‘ am o l " 1)

AG*

( K J m o l - 1 )

P y r i d i n e 3 2 . 4 2 9 . 7 - 1 1 5 . 8 6 1 . 3

P o l y m e r 5 / 1 2 2 . 7 2 1 . 1 - 1 3 7 . 6 9 5 9 . 8

P o l y m e r 1 0 / 1 2 0 . 2 2 0 . 8 - 1 3 1 . 9 6 6 0 . 1

The a c t i v a t i o n e n e r g i e s o f t h e p y r i d i n e c o n t a i n i n g

p o l y m e r s , w h i l e l o w e r t h a n t h e v a l u e f o r m o n o m e r i c p y r i d i n e , a r e

e s s e n t i a l l y t h e same r e g a r d l e s s o f t h e l o a d i n g . When two

r e a c t i o n s o f s i m i l a r a c t i v a t i o n e n e r g i e s a r e s t u d i e d a t t h e same

t e m p e r a t u r e a n d f o u n d t o p r o c e e d a t d i f f e r e n t r a t e s , t h e r e m u s t

b e a d i f f e r e n c e i n t h e i r e n t r o p y o f a c t i v a t i o n . H o w e v e r , t h e

e n t r o p i e s a r e a l l w i t h i n e x p e r i m e n t a l e r r o r o f e a c h o t h e r . The

n e g a t i v e v a l u e o f AS+ i n d i c a t e s t h e a s s o c i a t i v e n a t u r e o f t h e

t r a n s i t i o n s t a t e . The v a l u e s o f t h e G i b b s f r e e e n e r g y o f

a c t i v a t i o n a r e t h e s ame a l s o , s o t h e r e i s n o d i f f e r e n c e i n t h e

s p o n t a n e i t y o f t h e p r o c e s s e s r e g a r d l e s s o f w h e t h e r t h e p y r i d i n e

i s p o l y m e r i c o r m o n o m e r i c i n n a t u r e .

The v a r i a t i o n i n k w i t h p y r i d i n e c o n c e n t r a t i o n d o e s n o tob st h e r e f o r e r e s u l t f r o m a t h e r m o d y n a m i c e f f e c t . A d i f f e r e n t AG*

f o r t h e s e p r o c e s s e s was e x p e c t e d , b u t s u r p r i s i n g l y , t h e y w e r e

a l l w i t h i n e x p e r i m e n t a l e r r o r . As i s p r o p o r t i o n a l t o AG* a n d

78

k = [ p y r i d i n e ] k , i t i s p r o p o s e d t h a t t h i s v a r i a t i o n i s aobs 2r e f l e c t i o n o f e f f e c t i v e p y r i d i n e c o n c e n t r a t i o n a s o p p o s e d t o

c a l c u l a t e d p y r i d i n e c o n c e n t r a t i o n . One p o s s i b i l i t y i s t h a t t h e

t u n g s t e n h e x a c a r b o n y l d i f f u s e s i n t o t h e p o l y m e r c o i l s i n

s o l u t i o n w h e r e t h e e f f e c t i v e p y r i d i n e i s h i g h e r t h a n t h a t o f

f r e e p y r i d i n e i n s o l u t i o n , a n d a s a r e s u l t t h e l o c a l p y r i d i n e

c o n c e n t r a t i o n i n t h e v i c i n i t y o f t h e r e a c t i o n c e n t r e may b e h i g h

b e c a u s e o f p o l y m e r c o i l i n g . At h i g h e r p y r i d i n e l o a d i n g a

p r o x i m i t y e f f e c t may e x i s t w h e r e a h i g h f r e q u e n c y f a c t o r c o u l d

o p e r a t e f o r p y r i d i n e - t u n g s t e n c a r b o n y l e n c o u n t e r s . The e f f e c t i v e

c o n c e n t r a t i o n w o u l d b e g r e a t e r i n a p o l y m e r o f h i g h e r l o a d i n g o f

b o u n d p y r i d i n e , a n d a s a r e s u l t t h e s e c o n d o r d e r r a t e c o n s t a n t

w o u l d b e l a r g e r .

P i t t m a n p u t f o r w a r d a s i m i l a r e x p l a n a t i o n t o e x p l a i n t h e

d e c r e a s e d c a t a l y t i c a c t i v i t y o f a p o l y s t y r e n e a n c h o r e d r h o d i u m

h y d r o f o r m y l a t i o n c a t a l y s t 13 . He f o u n d t h a t t h e a c t i v i t y

d e c r e a s e d a s t h e b o u n d p p h 2 t o Rh r a t i o i n c r e a s e d . He s u g g e s t e d

t h a t t h e e f f e c t i v e c o n c e n t r a t i o n o f t h e b o u n d p h o s p h i n e u n i t s i s

g r e a t e r i n t h e a n c h o r e d s y s t e m r e l a t i v e t o d i s s o l v e d PPh , a n d3

c o n s e q u e n t l y e x c e s s b o u n d p h o s p h i n e c a n c o n t a c t t h e c a t a l y t i c

s i t e s d e c r e a s i n g t h e c o n c e n t r a t i o n o f c o o r d i n a t i v e l y u n s a t u r a t e d

r h o d i u m i n t e r m e d i a t e s a v a i l a b l e f o r c a t a l y s i s .

T h i s s t u d y p r o v i d e s i m p o r t a n t i n f o r m a t i o n on t h e r e a c t i o n

k i n e t i c s o f m e t a l c a r b o n y l s w i t h p o l y m e r i c s u p p o r t s c o n t a i n i n g

p e n d a n t s i t e s . To o u r k n o w l e d g e t h i s i s t h e f i r s t o f s u c h

i n v e s t i g a t i o n s .

79

T a b l e 2 . 4 . 3 E x p e r i m e n t a l d a t a f o r t h e d e t e r m i n a t i o n o f t h e a c t i v a t i o n p a r a m e t e r s f o r t h e f o r m a t i o n o f W(CO) ( p y r i d i n e ) f o r

52X10-ZM p y r i d i n e i n t o l u e n e .

Temp (K) 1 / T (K~ 1 ) ( X 1 0 " 3 )

k k ( s _ 1 ) o b s I n k o b s I n k / To b s

285 3 . 5 1 2 0 . 0 6 2 . 9 9 - 2 . 65288 3 . 4 7 2 1 . 5 6 3 . 0 7 - 2 . 5 9293 3. 41 27 . 73 3 . 3 2 - 2 . 3 6298 3 . 3 6 2 9 . 3 6 3 . 3 8 - 2 . 3 2303 3 . 30 4 4 . 62 3 . 8 0 - 1 . 92308 3 . 2 5 5 2 . 2 9 3 . 96 - 1 . 7 7313 3 . 1 9 5 9 . 8 5 4 . 0 9 - 1 . 65318 3 . 1 4 8 8 . 43 4 . 4 8 - 1 . 28323 3 . 1 0 8 9 . 0 4 4 . 4 9 - 1 . 2 9

A r r h e n i u s P l o t E y r i n g P l o t

S l o p e = - 3 8 9 1 ± 1 9 6 . 0 7 I n t e r c e p t = 1 6 . 5 9 ± 8 . 0 6 E - 2 C o r r e l a t i o n = 0 . 9 9

E* = 3 2 . 3 5 ± 1 . 6 3 KJ m o l " 1

S l o p e = - 3 5 7 4 . 4 ± 1 9 9 . 4 1 I n t e r c e p t = 9 . 8 3 ± 8 . 2 0 E - 2 C o r r e l a t i o n = 0 . 9 9

AH* = 2 9 . 7 2 ± 1 . 6 6 K J m o l " 1 AS* = - 1 1 5 . 8 4 ± 25 J K ^ m o l " 1

80

F i g . 2 . 4 . 5 A r r h e n i u s p l o t f o r t h e f o r m a t i o n o f W(CO) ( p y r i d i n e )5on t h e p h o t o l y s i s o f W(CO) i n t o l u e n e i n t h e p r e s e n c e o f

6

2X10“ZM p y r i d i n e .

In k0b8

1 / T ( X 1 0 E - 3 )

F i g . 2 . 4 . 6 E y r i n g p l o t f o r t h e f o r m a t i o n o f W(CO) ( p y r i d i n e ) on5

t h e p h o t o l y s i s o f W(CO) i n t o l u e n e i n t h e p r e s e n c e o f 2X10-ZM6

p y r i d i n e .

1/T (X10E-3)

81

T a b l e 2 . 4 . 4 E x p e r i m e n t a l d a t a f o r t h e d e t e r m i n a t i o n o f a c t i v a t i o n p a r a m e t e r s f o r t h e f o r m a t i o n o f W(CO)s ( p y r i d i n e ) f o r

2X10-2M p y r i d i n e i n a 5 / 1 c o p o l y m e r o f s t y r e n e a n d

4 - v i n y l p y r i d i n e .

Temp ( K) 1 / T ( K” 1 ) ( X 1 0 “ 3 )

k ^ ( s ’ 1)o b 8I n k obs I n k / T

o b s

290 3 . 4 5 5 8 . 65 4 . 0 7 - 1 . 60295 3 . 3 9 7 1 . 7 6 4 . 27 - 1 . 41298 3 . 3 6 8 6 . 7 4 4 . 46 - 1 . 2 3303 3 . 3 0 9 5 . 67 4 . 5 6 - 1 . 1 5308 3 . 2 5 1 0 7 . 2 7 4 . 67 - 1 . 0 5313 3 . 1 9 1 2 2 . 7 3 4 . 8 1 - 0 . 9 4318 3 . 1 4 1 4 5 . 4 7 4 . 98 - 0 . 7 8323 3 . 1 0 1 5 6 . 6 2 5 . 0 5 - 0 . 7 3

A r r h e n i u s P l o t

S l o p e = - 2 7 3 4 . 9 ± 1 8 1 . 8 I n t e r c e p t = 1 3 . 5 6 ± 5 . 7 7 E - 2 C o r r e l a t i o n = 0 . 9 9

E* = 2 2 . 7 4 ± 1 . 5 1 KJ m o l -1

E y r i n g P i o t

S l o p e = - 2 5 3 2 . 2 ± 2 3 1 . 5 1 I n t e r c e p t = 7 . 2 0 ± 6 . 0 5 E - 2 C o r r e l a t i o n = 0 . 9 9

AH* = 2 1 . 0 6 ± 1 . 9 2 K J m o l ' 1 AS* = - 1 3 7 . 6 9 ± 25 J K ^ m o l " 1

82

F i g . 2 . 4 . 7 A r r h e n i u s p l o t f o r t h e f o r m a t i o n o f W(CO) ( p y r i d i n e )5

on t h e p h o t o l y s i s o f W(CO) i n t o l u e n e i n t h e p r e s e n c e o f “ 62 X 1 0 ' 2M p y r i d i n e i n a 5 / 1 c o p o l y m e r o f s t y r e n e a n d

4 - v i n y l p y r i d i n e .

In k obt

1 / T ( X 1 0 E - 3 )

F i g . 2 . 4 . 8 E y r i n g p l o t f o r t h e f o r m a t i o n o f W(CO) ( p y r i d i n e ) on5

t h e p h o t o l y s i s o f W(CO) i n t o l u e n e i n t h e p r e s e n c e o f 2X10"ZM6

p y r i d i n e i n a 5 / 1 c o p o l y m e r o f s t y r e n e a n d 4 - v i n y l p y r i d i n e .

1/T (X10E-3)

83

T a b l e 2 . 4 . 5 E x p e r i m e n t a l d a t a f o r t h e d e t e r m i n a t i o n o f t h e

a c t i v a t i o n p a r a m e t e r s f o r t h e f o r m a t i o n o f W(CO) ( p y r i d i n e ) f o r ̂ 5

2X10"2M p y r i d i n e i n a 1 0 / 1 c o p o l y m e r o f s t y r e n e a n d

4 - v i n y l p y r i d i n e .

Temp (K) 1 / T ( K " 1 ) ( X 1 0 - 3 )

k *o b 8I n k

o b sI n k / T

o b 8

323 3 . 1 0 3 5 4 . 2 5 5 . 8 7 0 . 0 9318 3 . 1 4 2 8 1 . 4 6 5 . 6 4 - 0 . 1 2313 3 . 1 9 2 6 5 . 0 7 5 . 5 8 - 0 . 1 7308 3 . 2 5 2 2 1 . 4 1 5 . 4 0 - 0 . 3 3303 3 . 3 0 1 8 4 . 9 3 5 . 2 2 - 0 . 4 8298 3 . 3 6 1 7 5 . 9 1 5 . 1 7 - 0 . 5 3293 3 . 4 1 1 4 8 . 4 1 5 . 0 0 - 0 . 6 8289 3 . 46 1 2 5 . 2 1 4 . 8 3 - 0 . 8 4

A r r h e n i u s P l o t

S l o p e = - 2 4 3 1 . 9 ± 1 8 6 . 8 I n t e r c e p t = 1 3 . 2 8 ± 4 . 6 2 E - 2 C o r r e l a t i o n = 0 . 9 9

E* = 2 0 . 2 2 ± 1 . 5 5 KJ m o l " 1a

E v r i n q P l o t

S l o p e = - 2 4 7 5 . 9 ± 2 1 7 . 2 8 I n t e r c e p t = 7 . 7 4 ± 7 . 0 9 E - 2 C o r r e l a t i o n = 0 . 9 9

AH* = 2 0 . 7 7 ± 1 . 8 1 K J m o l ” 1 AS* = - 1 3 1 . 9 6 ± 25 J K " 1m o l ~ 1

84

on t h e p h o t o l y s i s o f W(CO) i n t o l u e n e i n t h e p r e s e n c e o f6

2X10”2M p y r i d i n e i n a 1 0 / 1 c o p o l y m e r o f s t y r e n e a n d

4 - v i n y l p y r i d i n e .

Fig.2.4.9 Arrhenius plot for the formation of W(C0)5(pyridine)

3.1 3.16 3.2 3.26 3,3 3.36 3,4 3.45

1 / T ( X 1 0 E - 3 )

F i g . 2 . 4 . 1 0 E y r i n g p l o t f o r t h e f o r m a t i o n o f W(CO) ( p y r i d i n e ) on5

t h e p h o t o l y s i s o f W(CO) i n t o l u e n e i n t h e p r e s e n c e o f 2X10" M6

p y r i d i n e i n a 1 0 / 1 c o p o l y m e r o f s t y r e n e a n d 4 - v i n y l p y r i d i n e .

1/T (X10E-3)

85

2 . 5 C o n c l u s i o n s

The s y n t h e s e s o f s u i t a b l e p o l y m e r i s a b l e l i g a n d s a n d m e t a l

c a r b o n y l c o n t a i n i n g p o l y m e r s y s t e m s was d i s c u s s e d . P o l y m e r - b o u n d

m e t a l c a r b o n y l s a r e c o n v e n i e n t l y p r e p a r e d by one o f t w o m e t h o d s :

t h e f i r s t i n v o l v i n g t h e p r e p a r a t i o n o f a m e t a l c a r b o n y l

c o n t a i n i n g monomer by r e a c t i o n w i t h p h o t o g e n e r a t e d [W(CO) (THF) ]5

f o l l o w e d by s u b s e q u e n t c o p o l y m e r i s a t i o n , a n d t h e s e c o n d

i n v o l v i n g d i r e c t r e a c t i o n o f p h o t o g e n e r a t e d [W(CO) ( TH F) ] w i t h a5

p r e f o r m e d c o p o l y m e r . P o l y m e r i s a t i o n s w e r e c a r r i e d o u t by

f r e e - r a d i c a l p o l y m e r i s a t i o n s i n t h e a b s e n c e o f s o l v e n t t o g i v e

n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n p o l y m e r s w i t h h i g h m e t a l

i n c o r p o r a t i o n .

The p r e s e n c e o f t h e m e t a l c a r b o n y l m o i e t y was c o n f i r m e d by

i n f r a r e d a n d U V / v i s a b s o r p t i o n s p e c t r o s c o p y . The p o l y m e r

a n c h o r e d m e t a l c a r b o n y l s e x h i b i t e d s t r o n g b a n d s i n t h e c a r b o n y l

s t r e t c h i n g f r e q u e n c y o f t h e i n f r a r e d s p e c t r u m , a n d t h e b o u n d

s p e c i e s w e r e r e a d i l y c h a r a c t e r i s e d on t h e b a s i s o f t h e p o s i t i o n

a n d n u mb e r o f t h e s t r e t c h i n g f r e q u e n c i e s . The s p e c t r a w e r e f o u n d

t o b e s i m i l a r t o t h o s e o f t h e i r m o n o m e r i c a n a l o g u e s . T h o s e

c o p o l y m e r s f o r m e d by r e a c t i o n o f [W(CO) (THF) ] w i t h a c o p o l y m e r

o f s t y r e n e a n d 4 - v i n y l - 4 ' - m e t h y l - 2 , 2 ' - b i p y r i d y l ( V b i p y )

e x h i b i t e d i n f r a r e d b a n d s o f t h e e x p e c t e d c i s - t e t r a c a r b o n y l

s p e c i e s , a n d a l s o b a n d s a t t r i b u t a b l e t o t h e p e n t a c a r b o n y 1, w h i l e

a c o p o l y m e r o f s t y r e n e a n d [W(CO) V b i p y ] s ho ws o n l y c a r b o n y l

s t r e t c h i n g b a n d s d u e t o t h e t e t r a c a r b o n y 1 s p e c i e s . The MLCT

e l e c t r o n i c a b s o r p t i o n b a n d s o f a c o p o l y m e r s o f

86

[W(CO) ( 4 - v i n y l p y r i d i n e ) ] w e r e s e n s i t i v e t o b o t h t h e s o l v e n t a nd5

t h e c o m p o s i t i o n o f t h e p o l y m e r b a c k b o n e . T h o s e c o p o l y m e r s o f

s t y r e n e a n d [W(CO) ( V b i p y ) ] e x h i b i t l ow e n e r g y MLCT t r a n s i t i o n s4

w h i c h s ho we d m a r k e d s o l v e n t d e p e n d e n c e .

The i n t e r a c t i o n o f t u n g s t e n c a r b o n y l w i t h c o p o l y m e r s o f

s t y r e n e a n d 4 - v i n y l p y r i d i n e i n t o l u e n e was i n v e s t i g a t e d u s i n g

l a s e r f l a s h p h o t o l y s i s . The r a t e s o f c o o r d i n a t i o n o f

p h o t o g e n e r a t e d [W(CO) ( t o l u e n e ) ] w e r e f o u n d t o b e h i g h e r f o r5

p o l y m e r - b o u n d p y r i d i n e a s o p p o s e d t o m o n o m e r i c p y r i d i n e i n

t o l u e n e . The r a t e s w e r e d e p e n d e n t on t h e l o a d i n g o f t h e

c o p o l y m e r s , t h e r a t e b e i n g h i g h e r f o r c o p o l y m e r s o f h i g h e r

l o a d i n g o f 4 - v i n y l p y r i d i n e t o s t y r e n e . T h i s d i f f e r e n c e i n r a t e s

was t h o u g h t t o b e a r e f l e c t i o n o f e f f e c t i v e p y r i d i n e

c o n c e n t r a t i o n , t h e e f f e c t i v e p y r i d i n e c o n c e n t r a t i o n b e i n g h i g h e r

i n t h e p o l y m e r c o i l s i n s o l u t i o n t h a n t h a t o f m o n o m e r i c

p y r i d i n e .

87

CHAPTER 3

THERMAL REACTIONS OF POLYMER-BOUND GROUP 6 METAL CARBONYLS

WHEN CAST AS FILMS.

88

3.1 Thermal Reactions of Polvmer-Bound Group 6. Metal Carbonyls

when C a s t a s F i 1ms

The t h e r m a l r e a c t i o n s o f t h e p o l y m e r - b o u n d m e t a l c a r b o n y l

compounds when c a s t a s f i l m s a n d t h e e f f e c t o f t h e p o l y m e r

b a c k b o n e on t h e t h e r m a l r e a c t i o n r o u t e s a v a i l a b l e a r e

i n v e s t i g a t e d u s i n g v a r i a b l e t e m p e r a t u r e i n f r a r e d s p e c t r o s c o p y .

The i n f l u e n c e o f p h y s i c a l p r o p e r t i e s s u c h a s t h e m o l a r m a s s a n d

t h e g l a s s t r a n s i t i o n t e m p e r a t u r e , T , w e r e i n v e s t i g a t e d . Thegi m p o r t a n c e o f t h e T^ on t h e o b s e r v e d t h e r m a l r e a c t i o n s a n d t h e

e f f e c t o f b i n d i n g t h e m e t a l c o m p l e x e s t o t h e p o l y m e r b a c k b o n e i s

e x a m i n e d u s i n g d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y (DSC) . The

p r o v i s i o n o f f r e e p e n d a n t b i n d i n g s i t e s on t h e p o l y m e r b a c k b o n e ,

t h e i m p o r t a n c e o f m e t a l l o a d i n g , a n d i n p a r t i c u l a r t h e e f f e c t o f

d i f f e r e n t p o l y m e r b a c k b o n e s i s a l s o i n v e s t i g a t e d . I n c l u d e d i s

e v i d e n c e f o r t h e d e c a r b o n y l a t i o n o f t h e p o l y m e r a n c h o r e d m e t a l

c a r b o n y l c o m p l e x e s r e s u l t i n g i n p o l y m e r s w h i c h c o n t a i n f u l l y

d e c a r b o n y l a t e d m e t a l c e n t r e s . The n a t u r e o f t h e t h e r m a l p r o d u c t s

a r e a l s o e x a m i n e d .

3 . 1 . 1 Thermal Substitution Reactions of G ro u p 6 Metal Ca rb on yl s.

I n g e n e r a l , m e t a l c a r b o n y l s a n d m e t a l c a r b o n y l c ompounds

c a n u n d e r g o s u b s t i t u t i o n r e a c t i o n s u n d e r e i t h e r t h e r m a l a n d / o r

p h o t o c h e m i c a l c o n d i t i o n s . T h e r m a l s u b s t i t u t i o n r e a c t i o n s o f

g r o u p 6 c a r b o n y l s a nd d e r i v a t i v e s o f t e n f o l l o w k i n e t i c s s i m i l a r

t o t h o s e o f t h e i r p h o t o c h e m i c a l s u b s t i t u t i o n r e a c t i o n s . The

h e x a c a r b o n y l s o f C r , Mo, a n d W u n d e r g o m e a s u r a b l e s u b s t i t u t i o n

88

a n d CO e x c h a n g e a t r e l a t i v e l y h i g h t e m p e r a t u r e s ( 1 0 0 - 1 7 0 ° C ) 25a .

The s u b s t i t u t i o n r e a c t i o n s o f [M(CO)g ( L ) ] u s u a l l y p r o c e e d by

l o s s o f L o r CO:

k[M(CO) ( L ) ] ---Ï—+ [M( CO) ] + L ( 1 )

5 5k

[M(CO) (L) ] + L ' -------* [M(CO) ( L ) ( L ' ) ] + CO ( 2 )5 4

R a t e = k [M(CO) ( L ) ] + k [M(CO) ( L ) ] . [ ( L ' ) ]1 5 2 5

The l i g a n d i n d e p e n d e n t f i r s t o r d e r p a t h d e s c r i b e d by k^ i s

c o n s i s t e n t w i t h l i g a n d d i s s o c i a t i o n t o f o r m a f i v e - c o o r d i n a t e

i n t e r m e d i a t e a s t h e r a t e d e t e r m i n i n g s t e p . The l i g a n d d e p e n d e n t

p a t h d e s c r i b e d by k 2 c o u l d i n v o l v e a t t a c k o f t h e l i g a n d a t

e i t h e r t h e c a r b o n y l c a r b o n o r m e t a l . I n a d d i t i o n , h o w e v e r , t h e

n a t u r e o f t h e l i g a n d L i n [M(CO) ( L ) ] c o m p l e x e s g r e a t l y5

i n f l u e n c e s t h e r e a c t i o n r a t e , e s p e c i a l l y t h e m a g n i t u d e o f k ,

t h e r a t e c o n s t a n t f o r t h e l i g a n d i n d e p e n d e n t t e r m . I n v i r t u a l l y

a l l c a s e s t h e r a t e o f t h e s u b s t i t u t i o n r e a c t i o n i s g r e a t e r when

L i s a n y l i g a n d o t h e r t h a n CO. The l i g a n d s w i t h g o o d a - d o n o r

a b i l i t y b u t p o o r r c - a c c e p t o r a b i l i t y show s i g n i f i c a n t l y f a s t e r

r a t e s t h a n t h o s e l i g a n d s c l o s e r t o CO i n b o n d i n g - t h e

T t - a c c e p t o r l i g a n d s ’ . The o r d e r o f l a b i l i s i n g a b i l i t y i s

C l " > NCO > Br > py > I > p p h 3 > CO. T h u s , i f L i s a h a l i d e

o r p y r i d i n e t h e r a t e o f CO d i s s o c i a t i o n f r o m [M(CO) ( L ) ] i s much5

g r e a t e r t h a n t h a t f o r M(CO)g .

The l a b i l i s i n g o f [M(CO) ( L ) ] by L i s i n v a r i a b l y o f5

c a r b o n y l l i g a n d s cis t o L, t h u s t h e i n c o m i n g l i g a n d i s i n i t i a l l y

89

i n t h e c i s p o s i t i o n . The c i s l a b i l i s a t i o n c o u l d b e b e c a u s e o f

t h e s t r e n g t h e n e d M-CO b o n d t r a n s t o L, e s p e c i a l l y f o r p o o r

7t - a c c e p t o r l i g a n d s . A l t e r n a t i v e l y , t h e f i v e - c o o r d i n a t e

i n t e r m e d i a t e s p e c i e s [M(CO) ( L ) ] c o u l d b e s t a b i l i s e d by p o o r4

r c - a c c e p t o r s o c c u p y i n g a b a s a l p o s i t i o n i n a s q u a r e p y r a m i d a l

i n t e r m e d i a t e , t h e r e b y f a c i l i t a t i n g t h e r e a c t i o n .

R e a c t i o n s o f [M(CO) ( L - L ) ] w i t h a l i g a n d , L , r e s u l t i n o ne4

o f t h r e e c o m p l e x e s n a m e l y f a c - o r m e r - [ M ( C 0 ) 3 ( L - L ) ( L ) ] ,

[M(CO) (L ) ] , o r [M(CO) (L ) ] 25 . W hi ch o f t h e s e c o m po u n d s i s4 2 3 3

f o r m e d d e p e n d s on t h e n a t u r e o f t h e c h e l a t e l i g a n d ( L - L ) a s t h e

s t r o n g e r l i g a n d s , s u c h a s 2 , 2 ' - b i p y r i d y l o r 1 , 1 0 - p h e n a n t h r o l i n e ,

t e n d t o b e r e t a i n e d a n d [ M ( C 0 ) 3 ( L - L ) ( L ) ] c o m p l e x e s f o r m e d w h i l e

w e a k e r l i g a n d s a r e d i s p l a c e d a n d [M(CO) (L ) ] f o r m e d . B u t t h e N4 2

d o n o r l i g a n d s a p p e a r t o g r e a t l y l a b i l i s e CO g r o u p s i n t h e

c o m p l e x . F o r a - d i i m i n e c o m p l e x e s s u c h a s t h o s e o f

2 , 2 ' - b i p y r i d y l , t h e d i s s o c i a t i o n o f CO f o r m s a f i v e - c o o r d i n a t e

c o m p l e x w h i c h r e a c t s w i t h L t o f o r m t h e p r o d u c t . E v i d e n c e

s t r o n g l y s u g g e s t s t h a t d i s s o c i a t i o n o c c u r s f r o m c a r b o n y l

p o s i t i o n s c i s t o t h e 2 , 2 ' - b i p y r i d y l l i g a n d .

The t h e r m a l c h e m i s t r y o f g r o u p 6 m e t a l c a r b o n y l s i s

p a r t i c u l a r l y i m p o r t a n t i n s y n t h e t i c a p p l i c a t i o n s a n d i n t h e

u n d e r s t a n d i n g o f t h e i r s u b s t i t u t i o n r e a c t i o n k i n e t i c s . H o w e v e r ,

m o r e r e c e n t l y much g r e a t e r a t t e n t i o n h a s b e e n p a i d t o t h e i r

p h o t o c h e m i c a l r e a c t i v i t y . P h o t o c h e m i c a l s u b s t i t u t i o n r e a c t i o n s

a r e u s e d m o r e w i d e l y i n t h e p r e p a r a t i o n o f m e t a l c a r b o n y l

90

d e r i v a t i v e s b e c a u s e o f t h e i r h i g h q u a n t u m y i e l d s , a n d b e c a u s e

t h e h i g h t e m p e r a t u r e s a n d l o n g r e a c t i o n t i m e s e m p l o y e d i n

t h e r m a l s y n t h e s e s o f t e n g i v e r i s e t o d e c o m p o s i t i o n o f c o m p l e x e s .

The a d v a n c e m e n t s a n d d e v e l o p m e n t i n p h o t o c h e m i c a l p r o c e d u r e s a n d

e q u i p m e n t h a v e m e a n t t h a t mo r e a t t e n t i o n h a s b e e n c o n c e n t r a t e d

i n t h i s a r e a . I n t h i s s t u d y o f t h e t h e r m a l r e a c t i o n s o f

p o l y m e r - b o u n d m e t a l c a r b o n y l s , we w e r e i n t e r e s t e d i n t h e t h e r m a l

g e n e r a t i o n o f c o o r d i n a t i v e l y u n s a t u r a t e d s p e c i e s i n s o l i d

s a m p l e s a nd w e r e c u r i o u s t o i n v e s t i g a t e t h e i n f l u e n c e o f t h e

p o l y m e r m a t r i x on t h e o b s e r v e d t h e r m a l r e a c t i o n s .

3.1.2 Colloidal Metal Dispersions in Po l y m e r s .

O r g a n i c p o l y m e r s c o n t a i n i n g m e t a l c a r b o n y l f u n c t i o n s a r e o f

p a r t i c u l a r i n t e r e s t b e c a u s e t h e i r d e c o m p o s i t i o n c o u l d f r e e

m e t a l s o r m e t a l o x i d e s w i t h i n t h e p o l y m e r . S u c h a d e c o m p o s i t i o n

i s a p p l i c a b l e t o t h e s y n t h e s i s o f a " s o l u t i o n o f m e t a l o r m i x e d

o x i d e " w i t h i n t h e p o l y m e r m a s s . M i x i n g m e t a l o x i d e s i n t o

p o l y m e r s r e s u l t s o n l y i n h e t e r o g e n e o u s c o m p o s i t e m a t e r i a l s s i n c e

t h e p a r t i c l e s i z e o f t h e m e t a l o x i d e s c a n n o t b e i n f i n i t e l y

r e d u c e d . S i n c e t h e s e c o m p o s i t i o n s a r e m e c h a n i c a l l y b l e n d e d , i t

i s a m a j o r t e c h n o l o g i c a l p r o b l e m t o c o n t r o l t h e u n i f o r m i t y o f

t h e d i s p e r s i o n a nd t h e s i z e o f t h e m e t a l l i c a g g r e g a t e s . As a

r e s u l t , t h e r m a l d e c o m p o s i t i o n s o f p o l y m e r a n c h o r e d t r a n s i t i o n

m e t a l c a r b o n y l s o f f e r s a c o m p l e m e n t a r y m e t h o d t o g e n e r a t e m e t a l

o x i d e p a r t i c l e s t h a t a r e h o m o g e n e o u s l y d i s p e r s e d a t t h e

m o l e c u l a r 1e v e l .

91

M e t a l l i c s p e c i e s c r e a t e d by UV p h o t o l y s i s , t h e r m a l o r

e l e c t r o n beam d e c o m p o s i t i o n i n a p o l y m e r m a t r i x s h o u l d b e h i g h l y

r e a c t i v e 8 8 . T h e r e a r e two m a j o r p a t h w a y s f o r c h e m i c a l r e a c t i o n

a v a i l a b l e f o r t h e s e s p e c i e s : ( i ) m e t a l i o n s / r a d i c a l s c a n a t t a c k

t h e p o l y m e r , a p r o c e s s t h a t c a n l e a d t o v a r i o u s p o l y m e r

d e g r a d a t i o n , c r o s s l i n k i n g , o r m e t a l a t t a c h m e n t p r o c e s s e s , a n d

( i i ) m e t a l s p e c i e s c a n a g g r e g a t e t o f o r m v e r y s m a l l c l u s t e r s

1 0 - 1 0 0 A i n d i a m e t e r . B o t h p r o c e s s e s may o c c u r a n d may b e

s i g n i f i c a n t l y i n f l u e n c e d by r e d u c i n g o r o x i d a t i v e a t m o s p h e r e s .

The c h e m i s t r y o f t h e s y s t e m , t h e r e l a t i v e i m p o r t a n c e o f t h e two

p r o c e s s e s , i s d e t e r m i n e d by t h e s t r u c t u r e o f t h e s o l i d p o l y m e r

m a t r i x a n d by t h e r a t e o f d e c o m p o s i t i o n p r o c e s s a s c o m p a r e d t o

t h e d i f f u s i o n t i m e o f t h e a c t i v e m e t a l s p e c i e s i n t h e s o l i d

p o l y m e r m a t r i x .

The i n t e r e s t i n t h i s a r e a i s b e c a u s e c o l l o i d a l m e t a l s h a v e

p r o v e d v e r y e f f i c i e n t i n many c a t a l y t i c p r o c e s s e s a n d f i n d o t h e r

a p p l i c a t i o n s i n m a g n e t i c m e d i a s t o r a g e , c o n d u c t i n g a n d

s e m i - i n s u l a t i n g p o l y m e r s , a n d p o l y m e r s w i t h s p e c i a l m e c h a n i c a l

p r o p e r t i e s . The v a s t m a j o r i t y o f s t u d i e s o f t h e t h e r m a l

r e a c t i o n s o f m e t a l c a r b o n y l c o m p l e x e s b o u n d t o p o l y m e r s u p p o r t s

h a v e b e e n c o n c e r n e d w i t h d i s p e r s i n g m e t a l s i n p o l y m e r i c

m a t e r i a l s . I t s e e m s a c o n v e n i e n t r o u t e t o t h e p r o d u c t i o n o f

t h e s e d i s p e r s i o n s by r e l a t i v e l y s i m p l e a n d i n e x p e n s i v e m e a n s .

D i s p e r s i o n s o f a v a r i e t y o f m e t a l s w i t h i n a n u m b e r o f d i f f e r e n t

p o l y m e r s y s t e m s h a v e b e e n r e p o r t e d .

92

P o l y m e r s c o n t a i n i n g a t t a c h e d rj6- ( a r e n e ) C r ( C O ) 3 m o i e t i e s

h a v e b e e n t h e r m a l l y d e c o m p o s e d t o p r o d u c e c h r o m i u m o x i d e

R 3 - 5 6 6 0 » 5 3p a r t i c l e s w i t h i n t h e p o l y m e r m a t r i x " ' . P i t t m a n e t a l .

d e m o n s t r a t e d t h a t t h e r m a l d e c o m p o s i t i o n o f rç - ( a r y l ) - C r ( C 0 ) 3

u n i t s p r o d u c e d m i x e d o x i d e s i m b e d d e d i n h i g h l y c r o s s l i n k e d

p o l y s t y r e n e p o l y m e r s , a n d t h a t s i m i l a r s i l o x a n e c o n t a i n i n g

7t - c o m p l e x e d c h r o m i u m t r i c a r b o n y l p o l y m e r s l i b e r a t e d CO b e t w e e n

100 a n d 200°C t o g i v e C r 20 35S. I n t h e r m a l d e c o m p o s i t i o n s o f

(i7 1- b e n z y l ) - ( r i 5- c y c l o p e n t a d i e n y l ) t r i c a r b o n y l m o l y b d e n u m a n d i t ’ s

t u n g s t e n a n a l o g u e a t t a c h e d t o t h e m a t r i x by a c a r b o n - t o - m e t a l

(T-bond, d e c o m p o s i t i o n s w e r e f o u n d t o p r o c e e d m o r e e f f i c i e n t l y i n

s o l u t i o n t h a n i n t h e a b s e n c e o f s o l v e n t b e c a u s e o f d e c r e a s e d

63m o b i l i t y o f r a d i c a l s when s a m p l e s w e r e n e a t . H e a t i n g s a m p l e s

o f c o p o l y m e r s o f v i n y l c y c l o p e n t a d i e n y l m a n g a n e s e t r i c a r b o n y l

r e s u l t e d i n CO e v o l u t i o n t o p r o d u c e c r o s s l i n k e d p o l y m e r s

c o n t a i n i n g f r e e m a n g a n e s e 60 .

T he a b o v e e x a m p l e s i n v o l v e t h e r m a l d e c o m p o s i t i o n s s t u d i e s

o f p o l y m e r - b o u n d m e t a l c a r b o n y l c o m p l e x e s . I n a n e x t e n s i v e

s t u d y , T a n n e n ba um e t a I . 88 i n v e s t i g a t e d t h e d e c o m p o s i t i o n o f

i r o n c a r b o n y l s i n s o l i d p o l y m e r m a t r i c e s i n a n a t t e m p t t o

p r e p a r e n o v e l m e t a l - p o l y m e r c o m p o s i t e s . I n h i s a p p r o a c h h e

p r e p a r e d d i s p e r s i o n s o f m e t a l s by i n s i t u p h a s e - s e p a r a t i o n i n a

s o l i d p o l y m e r m a t r i x u n d e r c o n t r o l l e d c o n d i t i o n s . The

o r g a n o m e t a l l i e c o m p l e x e s w e r e d i s s o l v e d i n p o l y m e r s o l u t i o n s t o

f o r m h o m o g e n e o u s m i x t u r e s . T h e s e s o l u t i o n s w e r e t h e n c a s t a n d

t h e r e s u l t i n g f i l m s e x p o s e d t o t h e r m a l , p h o t o l y t i c o r e l e c t r o n

93

beam e n e r g y . T h e s e t r e a t m e n t s d e c o m p o s e d t h e o r g a n o m e t a l 1 i c

c o m p l e x t o f o r m f i n e u n i f o r m d i s p e r s i o n s o f m e t a l o r m e t a l o x i d e

p a r t i c l e s ( 5 0 - 5 0 0 A ) i n t h e p o l y m e r m a t r i x . I t was s u g g e s t e d

t h a t t h e s e m a t e r i a l s may b e d e s i g n e d t o e x h i b i t n o v e l c a t a l y t i c

a c t i v i t y a n d a l s o t h a t t h e t e c h n i q u e d e s c r i b e d c o u l d b e o f v a l u e

f o r d e v e l o p m e n t o f n o v e l s o l i d m a t r i x i s o l a t i o n m e t h o d s t o

s u b s t i t u t e f o r c o n v e n t i o n a l g a s m a t r i c e s f o r i n f r a r e d m a t r i x

i s o l a t i o n s t u d i e s o f e x c i t e d a t o m i c o r m o l e c u l a r s p e c i e s .

T h e r m o l y s i s o f t r a n s i t i o n m e t a l c a r b o n y l s i n s o l v e n t s u n d e r

an i n e r t a t m o s p h e r e i s a w e l l known t e c h n i q u e f o r t h e

89p r e p a r a t i o n o f p u r e m e t a l p o w d e r s . S m i t h e t a 1. s u c c e s s f u l l y

a p p l i e d t h i s m e t h o d t o t h e f o r m a t i o n o f s t a b l e c o l l o i d a l

d i s p e r s i o n s ( 5 0 - 1 5 0 A) o f z e r o v a l e n t i r o n by t h e r m o l y s i s o f

Fe(CO) i n d i l u t e p o l y m e r s o l u t i o n s . S m i t h , i n a l a t e r r e p o r t ,5

d e v e l o p e d a m e t h o d f o r t h e p r e p a r a t i o n o f a h o m o g e n e o u s ,

p h y s i c a l l y s t a b l e c o l l o i d a l e l e m e n t a l t r a n s i t i o n m e t a l

d i s p e r s i o n c o m p r i s i n g o f m e t a l p a r t i c l e s h a v i n g a p a r t i c l e s i z e

w i t h i n t h e r a n g e o f 1 0 - 2 0 0 A d i s p e r s e d i n a n i n e r t l i q u i d a n d

s t a b i l i s e d by t h e p r e s e n c e o f a f u n c t i o n a l p o l y m e r t o t h e

9 0r e a c t i v e s i t e s o f w h i c h t h e m e t a l p a r t i c l e s a r e b o u n d . The

m e t h o d i n v o l v e d p r e p a r i n g a s o l u t i o n o f a f u n c t i o n a l p o l y m e r i n

a n i n e r t s o l v e n t , a n d i n c r e m e n t a l l y a d d i n g a g r o u p 6 m e t a l

h e x a c a r b o n y l p r e c u r s o r , a t a t e m p e r a t u r e o f 1 0 0 - 2 0 0 ° C a t w h i c h

t h e m e t a l c a r b o n y l p r e c u r s o r b e c o m e s b o u n d t o t h e p o l y m e r a n d

t h e r m a l l y d e c o m p o s e s t o p r o d u c e e l e m e n t a l t r a n s i t i o n m e t a l

p a r t i c l e s , t h e p r o c e s s b e i n g c a r r i e d o u t i n a n i n e r t a t m o s p h e r e .

94

The f u n c t i o n a l p o l y m e r s u s e d i n c l u d e d c o p o l y m e r s o f s t y r e n e w i t h

a comonomer c o n t a i n i n g a b i n d i n g m o i e t y s u c h a s b u t a d i e n e ,

p a r a - s t y r y l d i p h e n y l p h o s p h i n e , a n d 4 - v i n y l p y r i d i n e . S u c h

d i s p e r s i o n s , i t was p r o p o s e d , c o u l d b e u s e d a s c a t a l y s t s , o r may

b e u s e d f o r t h e p r e p a r a t i o n o f s u p p o r t e d c o l l o i d a l t r a n s i t i o n

m e t a l c a t a l y s t s . The d i s p e r s i o n s may a l s o b e u s e d f o r t h e

p r e p a r a t i o n o f a b l a t i v e o p t i c a l r e c o r d i n g m e d i a .

I n o u r i n v e s t i g a t i o n o f p o l y m e r - b o u n d m e t a l c a r b o n y l s o n e

may e n v i s i o n t h a t t h e r m a l d e c o m p o s i t i o n o f t h e s e m a t e r i a l s c o u l d

f r e e g r o u p 6 m e t a l s , m e t a l o x i d e s , o r o r g a n o m e t a l 1 i c g r o u p s

w i t h i n t h e p o l y m e r m a t r i x .

95

3 . 2 T h e r m a l R e a c t i o n s o f M e t a l C a r b o n y l C o n t a i n i n g P o l y m e r s .

The p o l y m e r s w e r e c a s t a s f i l m s on a s a p p h i r e s u p p o r t f r o m

c h l o r o f o r m s o l u t i o n a n d m o u n t e d i n a v a r i a b l e t e m p e r a t u r e c e l l

f i t t e d w i t h s o d i u m c h l o r i d e w i n d o w s . The t e m p e r a t u r e o f t h e c e l l

was r a i s e d s l o w l y f r o m room t e m p e r a t u r e a n d t h e c h a n g e s i n t h e

c a r b o n y l s t r e t c h i n g f r e q u e n c y r e g i o n o f t h e i n f r a r e d

( 2 2 0 0 - 1 7 0 0 cm- 1 ) w e r e m o n i t o r e d . The t h i c k n e s s o f t h e p o l y m e r

f i l m c o u l d b e v a r i e d by c h a n g i n g t h e v o l u m e o r c o n c e n t r a t i o n o f

t h e c a s t i n g s o l u t i o n , t h u s t h e i n t e n s i t y o f t h e c a r b o n y l

s t r e t c h i n g b a n d s i n t h e i n f r a r e d s p e c t r u m c o u l d b e a d j u s t e d . A

s a p p h i r e s u p p o r t was c h o s e n b e c a u s e o f i t ' s r o b u s t n e s s a n d

r e s i s t a n c e t o t h e r m a l s h o c k . A l l v a r i a b l e t e m p e r a t u r e

e x p e r i m e n t s w e r e c a r r i e d o u t i n v a c u o . S y n t h e s e s o f p o l y m e r s a n d

a n y p r o c e d u r e s a r e e x p l a i n e d i n g r e a t e r d e t a i l i n s e c t i o n 5 .

3 . 2 . 1 Copolymers of Styrene a n d M ( C O ) r(vinylpyridine).oOn h e a t i n g a c o p o l y m e r o f s t y r e n e a n d [W(CO) ( 4 - v p ) ] ( 2 0 / 1

5

m o l e r a t i o ) t o t e m p e r a t u r e s i n e x c e s s o f 100°C, t h e c a r b o n y l

s t r e t c h i n g f r e q u e n c i e s o f t h e p e n t a c a r b o n y 1 s p e c i e s d e c r e a s e d i n

i n t e n s i t y a n d w e r e r e p l a c e d by new b a n d s ( 2 0 0 0 , 1 8 8 3 , 1 8 6 1 , a n d

1832 cm" ) w h i c h c a n b e a s s i g n e d t o c i s - d i s u b s t i t u t e d t u n g s t e n

t e t r a c a r b o n y l s p e c i e s 69 ( s e e F i g u r e s 3 . 2 . 1 a n d 3 . 2 . 2 ) . F u r t h e r

h e a t i n g t h e p o l y m e r r e s u l t e d i n l o s s o f t h e t e t r a c a r b o n y l b a n d s

t o g i v e a f u l l y d e c a r b o n y l a t e d p o l y m e r a t a r o u n d 150°C. The

b a n d s a s s i g n a b l e t o t h e t h e r m a l l y f o r m e d c i s - t e t r a c a r b o n y l a r e

c l o s e t o t h o s e r e p o r t e d f o r c i s - [ W ( C O ) ( p y r i d i n e ) ] ( 2 0 0 2 , 1 8 8 5 ,4 2

_ I 731 8 6 8 , a n d 1820 cm" i n n u j o l m u l l ) . As t h e r e a r e no

96

u n c o o r d i n a t e d p y r i d i n e u n i t s a v a i l a b l e on t h e p o l y m e r b a c k b o n e ,

a d i s s o c i a t i v e p r o c e s s i n v o l v i n g t h e f o r m a t i o n o f f r e e m e t a l

p e n t a c a r b o n y l m i g h t o c c u r . The f r e e p e n t a c a r b o n y l c o u l d r e a c t

w i t h a n o t h e r b o u n d p e n t a c a r b o n y l m o i e t y p r o d u c i n g m e t a l

h e x a c a r b o n y l a n d a m e t a l t e t r a c a r b o n y l c e n t r e , w h i c h c o u l d t h e n

c o o r d i n a t e two p e n d a n t b o u n d p y r i d i n e g r o u p s ( S c h e m e 3 . 1 ) . A

s i m i l a r r e a c t i o n h a s b e e n o b s e r v e d i n t h e t h e r m a l c o n v e r s i o n o f

[W(CO) ( d i p y r i d y l a m i n e ) ] t o [W(CO) ( d i p y r i d y l a m i n e ) ] i n t h e5 4

s o l i d s t a t e 20 .

S u c h a t h e r m a l r e a c t i o n i n v o l v i n g t h e f o r m a t i o n o f [M(CO) ]5

i s known t o o c c u r i n m e t a l c a r b o n y l s c o n t a i n i n g a m i n e l i g a n d s i n

s o l u t i o n 32 . [M(CO)5 ( a m i n e ) ] c o m p l e x e s t h e r m a l l y d e c o m p o s e by

l o s s o f t h e a m i n e a n d a b s t r a c t i o n o f CO by t h e r e a c t i v e

i n t e r m e d i a t e [M(CO) ] ( e q u a t i o n 3 ) .5

. [M(CO) ( a m i n e ) ][M(CO) ( a m i n e ) ] -------- ----- > M(CO) ------------------------------- »

5 5

M(CO) + d e g r a d a t i o n p r o d u c t s6

E q u a t i o n 3

F u r t h e r s p e c t r o s c o p i c e v i d e n c e f o r t h e o c c u r r e n c e o f t h i s

d i s p r o p o r t i o n a t i o n p r o c e s s was o b t a i n e d by i n v e s t i g a t i n g t h e

v o l a t i l e c o m p o n e n t s p r o d u c e d on h e a t i n g t h e c o p o l y m e r . T h e s e

e x p e r i m e n t s w e r e p e r f o r m e d u s i n g a v a r i a b l e t e m p e r a t u r e i n f r a r e d

g a s c e l l (10 cm p a t h l e n g t h ) . The s o l i d was i n t r o d u c e d i n t o t h e

c e l l a n d t h e n t h e c e l l was e v a c u a t e d a n d s e a l e d . The g a s e s

97

e v o l v e d upon h e a t i n g t h e s o l i d p o l y m e r w e r e t h e n d e t e r m i n e d by

i n f r a r e d s p e c t r o s c o p y a t v a r i o u s t e m p e r a t u r e s . On h e a t i n g t h e

s a m p l e t o a b o u t 10 0 ° C , b a n d s a t t r i b u t a b l e t o g a s e o u s W(CO)g

(T : 1998 cm-1 i n t h e g a s p h a s e 32) a n d c a r b o n m o n o x i d elu( 2 1 4 3 cm- 1 ) w e r e d e t e c t e d . T h e s e p r o d u c t s w o u l d b e e x p e c t e d i f a

d i s p r o p o r t i o n a t i o n p r o c e s s was o c c u r r i n g .

H e a t i n g a s i m i l a r c o p o l y m e r o f s t y r e n e a nd

[W(CO) ( 2 - v i n y l p y r i d i n e ) ] r e s u l t e d o n l y i n t h e l o s s o f a l l t h e5

c a r b o n y l b a n d s i n t h e c a r b o n y l r e g i o n o f t h e i n f r a r e d a t 130°C

( F i g u r e 3 . 2 . 3 ) , w i t h g a s e o u s t u n g s t e n h e x a c a r b o n y l a n d CO b e i n g

e v o l v e d . The d i f f e r e n c e i n t h e r m a l b e h a v i o u r b e t w e e n c o p o l y m e r s

o f 4 - v i n y l p y r i d i n e a n d 2 - v i n y l p y r i d i n e i s p r o b a b l y a r e s u l t o f

s i g n i f i c a n t s t e r i c h i n d r a n c e t o t h e c o o r d i n a t i o n o f t h e p y r i d i n e

i n c o p o l y m e r s o f 2 - v i n y l p y r i d i n e . C o n s e q u e n t l y , l o s s o f t h e

m e t a l c a r b o n y l f r a g m e n t a p p e a r s t o b e t h e o n l y t h e r m a l r o u t e

a v a i l a b l e t o c o p o l y m e r s o f 2 - v i n y l p y r i d i n e c o n t a i n i n g b o u n d

p e n t a c a r b o n y l m o i e t i e s . H o w e v e r , t r e a t m e n t o f a c o p o l y m e r o f

s t y r e n e a n d 2 - v i n y l p y r i d i n e ( 2 0 / 1 m o l e r a t i o ) w i t h l i t h i a t e d

912 - p i c o l i n e y i e l d e d a c o p o l y m e r w i t h p e n d a n t d i p y r i d y l m e t h a n e

m o i e t i e s ( Scheme 3 . 2 ) . R e a c t i o n o f t h i s p o l y m e r w i t h t h e

p h o t o c h e m i c a l l y g e n e r a t e d [W(CO)5 ( T H F ) ] p r o d u c e d a p o l y m e r w i t h

m e t a l p e n t a c a r b o n y l s p e c i e s b o u n d t o i t . Upon h e a t i n g t h i s

p o l y m e r t o o v e r 1 0 0 ° C , s p e c t r a l c h a n g e s c o n s i s t e n t w i t h t h e

t h e r m a l p r o d u c t i o n o f t h e c i s - t e t r a c a r b o n y 1 f r a g m e n t w e r e

o b s e r v e d . I t i s known t h a t d i p y r i d y l m e t h a n e h a s t h e a b i l i t y t o

a c t b o t h a s a m o n o d e n t a t e a n d a b i d e n t a t e l i g a n d , a n d e v i d e n c e

98

h a s b e e n r e p o r t e d w h i c h d e m o n s t r a t e s t h a t t h e r e l a t e d

d i - 2 - p y r i d y l a mi n e c o m p l e x [W(CO)5 ( d i p y a m ) ] c a n u n d e r g o a

c o n v e r s i o n f r o m m o n o d e n t a t e t o b i d e n t a t e c o o r d i n a t i o n i n t h e

s o l i d s t a t e 9 1 .

H e a t i n g c o p o l y m e r s o f s t y r e n e a n d [ C r ( CO ) ( 4 - v p ) ] ( 2 0 / 1

m o l e r a t i o ) t o t e m p e r a t u r e s o f g r e a t e r t h a n 100°C, r e s u l t e d o n l y

i n a d e c a r b o n y l a t e d p o l y m e r , no t e t r a c a r b o n y l b e i n g o b s e r v e d .

S i m i l a r e x p e r i m e n t s w i t h [Mo(CO) ( 4 - v p ) ] c o p o l y m e r s when h e a t e d5

e x h i b i t e d new b a n d s a t 2 0 0 8 , 1 8 8 6 , a n d 1 8 3 5 cm-1 a s s i g n a b l e t o

t h e c i s - t e t r a c a r b o n y l s p e c i e s ( c i s - [ M o ( C O ) ( p y ) ] : 2 0 0 2 , 1 8 9 9 ,5 2

1 8 7 1 , a n d 1828 cm” 1 i n n u j o l m u l l ) 7 3 . T h i s d i f f e r e n c e i n t h e r m a l

r e a c t i v i t y i s p r o b a b l y b e c a u s e o f t h e t h e r m a l i n s t a b i l i t y o f t h e

c h r o m i u m t e t r a c a r b o n y l s p e c i e s i n a c c o r d a n c e w i t h t h e s e q u e n c e

o f s t a b i l i t i e s o f g r o u p 6 m e t a l t e t r a c a r b o n y l s : Mo > W > C r .

99

F i g . 3 . 2 . 1 a C h a n g e s o b s e r v e d i n t h e 2 2 0 0 - 1 7 0 0 cm 1 r e g i o n o f t h e i n f r a r e d s p e c t r u m , u p o n h e a t i n g a c o p o l y m e r o f s t y r e n e a n d

[M(CO) ( 4 - v p ) ] (M = W o r Mo) . T h e s e c h a n g e s a r e c o n s i s t e n t w i t h5

t h e f o r m a t i o n o f a c i s - d i s u b s t i t u t e d t e t r a c a r b o n y l c o m p l e x .

2200 2100 2000 1900 1800 1700wavenumbers (cm- 1 )

The c h a r a c t e r i s t i c pentacarbonyl bands d e c r e a s e i n intensity at

100°C and a r e r e p l a c e d t h o s e o f t h e c i s -tetracarbonyl species,

a = 20°C , b = 125°C.

100

F i g . 3 . 2 . 1 b C h a n g e s o b s e r v e d i n t h e 2 2 0 0 - 1 7 0 0 cm 1 r e g i o n o f t h e

i n f r a r e d r e g i o n on f u r t h e r h e a t i n g . C o m p l e t e d e c a r b o n y l a t i o n o f

t h e m e t a l c e n t r e s o c c u r s on r a i s i n g t h e t e m p e r a t u r e t o 165°C.

2200 2100 2000 1300 1800 1700wavenumbers (cm- 1 )

The b a n d s o f t h e c i s - t e t r a c a r b o n y l d e c r e a s e i n i n t e n s i t y t o

e v e n t u a l l y leave a fully d e c a r b o n y l a t e d polymer,

c = 125°C, d = 165°C.

101

Scheme 3 . 1 P r o p o s e d m e c h a n i s m f o r t h e t h e r m a l r e a c t i o n r o u t e s o f

a c o p o l y m e r o f s t y r e n e a n d [ W( C0 )s ( 4 - v p ) ] .

102

F i g . 3 . 2 . 2 The c h a n g e s o b s e r v e d i n t h e c a r b o n y l s t r e t c h i n g

f r e q u e n c y r e g i o n o f t h e i n f r a r e d on h e a t i n g a c o p o l y m e r o f s t y r e n e a n d [W(CO) ( 2 - v i n y l p y r i d i n e ) ] . D e c a r b o n y l a t i o n o f t h e

5m e t a l c e n t r e s i s t h e o n l y t h e r m a l r e a c t i o n r o u t e a v a i l a b l e .

wavenumbers (cm- 1 )

The d i f f e r e n c e i n t h e r m a l b e h a v i o u r o f copolymers of 2- and

4-vinylpyridine is t h o u g h t t o d u e t o steric effects imposed by

the polymer backbone in those c o p o l y m e r s o f 2-vinylpyridine.

a = 25°C, b = 175°C.

Note the production of W(CO)^ (ca. 1975 c m ' 1) .

103

Scheme 3 . 2 The d e r i v a t i s a t i o n o f a c o p o l y m e r o f s t y r e n e a n d

2 - v i n y l p y r i d i n e u s i n g l i t h i a t e d 2 - p i c o l i n e , r e s u l t i n g i n a

c o o r d i n a t i n g p o l y m e r i n w h i c h t h e c o o r d i n a t i o n mode may b e

v a r i e d .

104

3.2.2 Polymers of Styrene and M ( C O ) 4 - v i n y l -4'-methyl-2,2'-bipy)

The t h e r m a l r e a c t i o n s o f c o p o l y m e r s c o n t a i n i n g c h e l a t i n g

c o o r d i n a t i n g s i t e s w e r e a l s o i n v e s t i g a t e d . C o p o l y m e r s o f s t y r e n e

a n d [M(CO) ( 4 - v i n y l - 4 ' - m e t h y l - 2 , 2 ’ - b i p y r i d y l ) ] (M = C r , Mo, o r4

W) w e r e p r e p a r e d a s d e s c r i b e d e a r l i e r . On h e a t i n g t h e s e p o l y m e r s

t o e l e v a t e d t e m p e r a t u r e s a d e c r e a s e i n t h e t e t r a c a r b o n y l b a n d s

was o b s e r v e d u n t i l a t 14 0 ° C , l o s s o f a l l c a r b o n y l s t r e t c h i n g

f r e q u e n c i e s o c c u r r e d , i n d i c a t i n g c o m p l e t e d e c a r b o n y l a t i o n o f t h e

m e t a l c a r b o n y l s p e c i e s f r o m t h e p o l y m e r ( s e e F i g u r e 3 . 2 . 3 ) .

H e a t i n g t h i s p o l y m e r i n a v a r i a b l e t e m p e r a t u r e i n f r a r e d g a s c e l l

t o 140°C a n d t h e s u b s e q u e n t e x a m i n a t i o n o f t h e g a s e s p r o d u c e d ,

c o n f i r m e d t h e p r e s e n c e o f b o t h m e t a l h e x a c a r b o n y l a n d f r e e

c a r b o n m o n o x i d e . T h i s s u g g e s t e d t h a t t h e t h e r m a l r e a c t i o n a g a i n

i n v o l v e d a d i s p r o p o r t i o n a t i o n p r o c e s s , w h i c h w o u l d r e s u l t i n

some o f t h e m e t a l c e n t r e s s u f f e r i n g d e c a r b o n y l a t i o n , w i t h

c o n c o m i t a n t f o r m a t i o n o f t h e m e t a l h e x a c a r b o n y l .

3.2.3 Thermal Reactions of Polymers of p-Styryldiphenylphosphine

C o p o l y m e r s o f s t y r e n e a n d p a r a - s t y r y l d i p h e n y l p h o s p h i n e w e r e

p r e p a r e d a n d r e a c t e d w i t h p h o t o c h e m i c a l 1 y p r o d u c e d

[M(CO)5 ( T H F ) ] . The r e s u l t i n g p o l y m e r s d i s p l a y e d c a r b o n y l b a n d s

o f b o t h t h e p e n t a c a r b o n y l a n d c i s - t e t r a c a r b o n y l s p e c i e s i n t h e

9 2i n f r a r e d s p e c t r u m . A t e l e v a t e d t e m p e r a t u r e s t h e p e n t a c a r b o n y l

f r e q u e n c i e s d e c r e a s e w i t h a n a c c o m p a n y i n g i n c r e a s e i n i n t e n s i t y

o f t h e t e t r a c a r b o n y l b a n d s u n t i l o n l y t e t r a c a r b o n y l a b s o r p t i o n s

r e m a i n ( F i g u r e 3 . 2 . 4 ) . D e c a r b o n y l a t i o n t h e n t a k e s p l a c e a t a b o u t

105

200°C. I n g e n e r a l , t h e t h e r m a l l y p r o d u c e d p h o s p h i n e

t e t r a c a r b o n y l s h a d g r e a t e r t h e r m a l s t a b i l i t y t h a n t h o s e o f t h e

n i t r o g e n c o n t a i n i n g p o l y m e r s . T h i s i s p r o b a b l y a c o n s e q u e n c e o f

26 32t h e b e t t e r l a b i l i s i n g a b i l i t y o f a m i n e s o v e r p h o s p h i n e s '

A n a l y s i s o f t h e v o l a t i l e s o f t h e t h e r m a l r e a c t i o n s h o w e d t h e

p r e s e n c e o f t h e m e t a l h e x a c a r b o n y l a n d CO. M o n o m e r i c p h o s p h i n e s

o f t h e t y p e [M(CO)4 ( P P h 3 ) 2 ] u s u a l l y f a v o u r t h e t r a n s i s o m e r , t h e

t r a n s d i s u b s t i t u t e d i s o m e r b e i n g m o r e t h e r m o d y n a m i c a l l y

s t a b l e 32' 9 2 . D a r e n s b o u r g 92b i n h i s s t u d y o f [Mo(CO) ( P P h ) ]4 3 2

f o u n d t h a t t h e c i s i s o m e r t h e r m a l l y r e a r r a n g e s c o m p l e t e l y t o t h e

t r a n s i s o m e r v i a a d i s s o c i a t i v e p r o c e s s i n v o l v i n g Mo-P b o n d

c l e a v a g e a t 6 0 - 80 °C i n s o l u t i o n . I n c o n t r a s t , t h e c i s i s o m e r was

f o r m e d t h e r m a l l y i n t h e c a s e o f p o l y m e r a n c h o r e d

[Mo(CO)4 ( P P h 3 ) 2 ] .

106

F i g . 3 . 2 . 3 C h a n g e s o b s e r v e d i n t h e c a r b o n y l s t r e t c h i n g f r e q u e n c y

r e g i o n o f t h e i n f r a r e d on h e a t i n g a c o p o l y m e r o f s t y r e n e a n d

[W(CO) ( 4 - v i n y l - 4 1- m e t h y l - 2 , 2 ' - b i p y r i d y l ) ] t o 150°C.4

2200 2100 2000 1900 1**0 1 TOP

wavenumbers (cm-1)Decarbonyl a t i o n i s t h e only available t h e r m a l r o u t e f o r

copolymers of s t y r e n e containing the g o o d chelating ligand

2 , 2 '-bipyridyl (M = C r , Mo, or W ) .

a =20°C,b=150°C.

107

F i g . 3 . 2 . 4 a C h a n g e s o b s e r v e d i n t h e i n f r a r e d s p e c t r u m

( 2 2 0 0 - 1 7 0 0 c m _1) u p o n h e a t i n g a t u n g s t e n c a r b o n y l c o n t a i n i n g

c o p o l y m e r o f s t y r e n e a n d p - s t y r y l d i p h e n y l p h o s p h i n e .

2200 2100 2000 1900 1800 1700wavenumbers ( c m ' 1)

T h e s e polymers contained both bound pentacarbonyl (2069,

1936 cm ) a n d cis-tetracarbonyl (2017, 1903 cm 1 , the band

e x p e c t e d at a r o u n d 1940 cm ^ 92c i s m a s k e d by the intense

pentacarbonyl fundamental absorption) species. On heating to

125°C the pentacarbonyl bands decrease with a concomitant

increase in intensity in the tetracarbonyl absorptions.

108

F i g . 3 . 2 . 4 b C h a n g e s o b s e r v e d i n t h e r e g i o n 2 2 0 0 - 1 7 0 0 c m ' 1 on

f u r t h e r r a i s i n g t h e t e m p e r a t u r e t o 200°C.

2200 2100 2 0 0 0 1900 1800 1700

wavenumbers (cm- 1 )

At 165°C t h e tetracarbonyl b a n d s (2011, 1934, 1885, and 1867

(sh) cm a r e resolved as the pentacarbonyl bands d e c r e a s e .

F u r t h e r heating to 200°C r e s u l t s i n decarbonylation of the metal

centers .

109

3.3 The Effect of the Chemical Composition of the PolymerB a c k b o n e on t h e T h e r m a l C h e m i s t r y .

On h e a t i n g c o p o l y m e r s o f s t y r e n e c o n t a i n i n g b o u n d g r o u p 6

m e t a l p e n t a - a nd t e t r a - c a r b o n y l m o i e t i e s b o u n d v i a n i t r o g e n o r

p h o s p h o r u s m e t a l b o n d s , t h e d e c a r b o n y l a t i o n o f t h e c a r b o n y l

s p e c i e s t o y i e l d a p o l y m e r c o n t a i n i n g f u l l y d e c a r b o n y l a t e d m e t a l

c e n t r e s was o b s e r v e d . I t was o f i n t e r e s t t o d e t e r m i n e w h e t h e r

c h e m i c a l p r o p e r t i e s c a n i n f l u e n c e t h e r e a c t i o n s o b s e r v e d on

h e a t i n g t h i n f i l m s o f t h e s e p o l y m e r s . I n t r o d u c i n g e x c e s s b i n d i n g

s i t e s , c h a n g i n g t h e m e t a l l o a d i n g , a n d e x a m i n i n g t h e e f f e c t s o f

d i f f e r e n t p o l y m e r b a c k b o n e c o m p o s i t i o n s may p r o v i d e u s w i t h a

c l e a r e r u n d e r s t a n d i n g o f t h e t h e r m a l b e h a v i o u r o f t h e s e

m a t e r i a l s . I t a l s o o f i m p o r t a n c e t o e x a m i n e t h e e f f e c t t h e s e

p a r a m e t e r s h a v e on t h e n a t u r e o f t h e f i n a l d e c a r b o n y l a t e d

p r o d u c t .

3 . 3 . 1 The E f f e c t o f C h a n g i n g t h e Polymer Backbone.

A l t e r a t i o n s i n t h e t h e c h e m i s t r y o f t h e comonomer w o u l d

o b v i o u s l y r e s u l t i n c o p o l y m e r s w i t h v a s t l y d i f f e r i n g c h e m i c a l

p r o p e r t i e s w h i c h i n t h e m s e l v e s may a f f e c t t h e t h e r m a l r e a c t i o n s

o f m e t a l c a r b o n y l m o i e t i e s b o u n d t o t h e m . F o r t h i s r e a s o n

c o p o l y m e r s o f [M(CO) ( 4 - v p ) ] a n d [M(CO) ( 4 - v i n y l - 4 ' -5 4

m e t h y l - 2 , 2 ' - b i p y ) ] w i t h m e t h y l m e t h a c r y l a t e a n d e t h y l a c r y l a t e

w e r e p r e p a r e d . The r e s u l t i n g c o p o l y m e r s h a v e o x y g e n s i t e s on t h e

p o l y m e r b a c k b o n e . O x y g e n , l i k e o t h e r f i r s t row e l e c t r o n e g a t i v e

e l e m e n t s p o s s e s s i n g l o n e p a i r s , f u n c t i o n s a s a c r - do no r l i g a n d i n

m e t a l c a r b o n y l c o m p l e x e s . The L e w i s b a s i c i t y o f o x y g e n i s l e s s

t h a n t h a t o f n i t r o g e n , a n d a s a c o n s e q u e n c e l i g a n d s b o n d i n g

1 1 0

t h r o u g h o x y g e n a r e l e s s e f f e c t i v e t h a n t h o s e b o n d i n g t h r o u g h

n i t r o g e n a n d i n m o s t c o m p l e x e s t h e o x y g e n l i g a n d i s r a t h e r

w e a k l y b o u n d 3 2 . H o w e v e r , o x y g e n s i t e s may a c t by s t a b i l i s i n g

t h e r m a l l y p r o d u c e d i n t e r m e d i a t e s .

H e a t i n g c o p o l y m e r s o f [M(CO) ( 4 - v p ) ] (M = Mo o r W) w i t h5

m e t h y l m e t h a c r y l a t e o r e t h y l a c r y l a t e t o e l e v a t e d t e m p e r a t u r e s

r e s u l t e d i n t h e f o r m a t i o n o f t h e c i s - t e t r a c a r b o n y l s p e c i e s

f o l l o w e d by d e c a r b o n y l a t i o n a t h i g h e r t e m p e r a t u r e s . I n s i m i l a r

c o p o l y m e r s w i t h M = C r , d e c a r b o n y l a t i o n was t h e o n l y t h e r m a l l y

o b s e r v e d e v e n t . D e c a r b o n y l a t i o n was t h e o n l y r o u t e a v a i l a b l e f o r

c o p o l y m e r s o f [M(CO) ( 4 - v i n y l - 4 ’ - m e t h y l - 2 , 2 ' - b i p y ) ] (M = C r , Mo,A

o r W) a n d m e t h y l m e t h a c r y l a t e o r e t h y l a c r y l a t e . M e t a l

h e x a c a r b o n y l a n d c a r b o n m o n o x i d e w e r e d e t e c t e d i n e a c h i n s t a n c e

on m o n i t o r i n g t h e v o l a t i l e s a b o v e t h e s a m p l e s a t e l e v a t e d

t e m p e r a t u r e s . The t h e r m a l r e a c t i o n s o f p o l y m e r f i l m s o f

m e t h y l m e t h a c r y l a t e a n d e t h y l a c r y l a t e a p p e a r t o b e s i m i l a r t o

t h e r e a c t i o n s o f t h e i r a n a l o g o u s s t y r e n e c o p o l y m e r s . T h e s e

f i n d i n g s i n d i c a t e t h a t d o n o r o x y g e n s i t e s on t h e p o l y m e r

b a c k b o n e do n o t p l a y a s i g n i f i c a n t r o l e i n s t a b i l i s i n g t h e m e t a l

c a r b o n y l f r a g m e n t s a t t h e s e t e m p e r a t u r e s .

3 . 3 . 2 Th e rm a l R e a c t i o n s o f Polymers with Free Pendant Sites.

A s e r i e s o f t e r p o l y m e r s o f s t y r e n e a n d [W(CO) ( 4 - v p ) ]5

( 2 0 / 1 m o l e r a t i o ) c o n t a i n i n g e x c e s s p e n d a n t p y r i d i n e w e r e

s y n t h e s i s e d , a n d t h e e f f e c t o f t h e s e a d d i t i o n a l b i n d i n g s i t e s on

t h e o b s e r v e d t h e r m a l r e a c t i v i t y i n v e s t i g a t e d . H e a t i n g p o l y m e r s

111

c o n t a i n i n g a n e x c e s s o f 4 - v i n y l p y r i d i n e o f 1 / 1 5 m o l e r a t i o o f

4 - v p / s t y r e n e o r g r e a t e r , r e s u l t e d i n t h e a p p e a r a n c e o f t h e

c i s - t e t r a c a r b o n y l b a n d s w i t h a c c o m p a n y i n g d e c r e a s e i n t h e

i n t e n s i t y o f t h e p e n t a c a r b o n y l f r e q u e n c i e s a t 100°C a s b e f o r e .

H o w e v e r , t h e s e t e t r a c a r b o n y l b a n d s w e r e r e p l a c e d by new b a n d s a t

1892 a n d 1765 cm-1 on f u r t h e r h e a t i n g t o 1 5 0 - 1 7 5 ° C ( s e e

F i g u r e 3 . 3 . 1 ) . T h e s e c a r b o n y l s t r e t c h i n g f r e q u e n c i e s a r e c l o s e

t o t h o s e r e p o r t e d f o r [Mo(CO)3 ( p y ) 3 ] ( 1 8 8 8 , 1746 c m ' 1 i n n u j o l

m u l l ) 93 , w h i c h h a s a f a c - c o n f i g u r a t i o n . T h e s e new b a n d s c a n b e

a s s i g n e d t o t h e t h e r m a l l y p r o d u c e d f a c - t r i c a r b o n y l c om p o un d ,

b o u n d v i a t h r e e p o l y m e r a n c h o r e d p y r i d i n e c o o r d i n a t i o n s i t e s .

F u r t h e r r a i s i n g t h e t e m p e r a t u r e r e s u l t e d i n l o s s o f t h e c a r b o n y l

b a n d s . T h o s e p o l y m e r s c o n t a i n i n g l o w e r c o n c e n t r a t i o n s o f e x c e s s

p y r i d i n e b e h a v e d a s b e f o r e w i t h p r o d u c t i o n o f t h e t e t r a c a r b o n y l

a n d e v e n t u a l d e c a r b o n y l a t i o n o f t h e m e t a l c e n t r e s .

An i d e n t i c a l e x p e r i m e n t was c o n d u c t e d w i t h c o p o l y m e r s o f

s t y r e n e a n d [W(CO) ( 4 - v p ) ] i n c o r p o r a t i n g f r e e p e n d a n t5

2 - v i n y l p y r i d i n e o n t o t h e p o l y m e r b a c k b o n e . The a d d i t i o n a l

2 - v i n y l p y r i d i n e r e s i d u e s h a d no e f f e c t on t h e t h e r m a l c h e m i s t r y .

A c o p o l y m e r o f 2 - v i n y l p y r i d i n e ( 2 0 / 1 m o l e r a t i o ) a nd

[W(CO) ( 4 - v p ) ] d i s p l a y s t h e same t h e r m a l r e a c t i v i t y a s a5

c o p o l y m e r o f s t y r e n e a n d [W(CO) ( 4 - v p ) ] , t h a t i s t e t r a c a r b o n y l5

f o r m a t i o n f o l l o w e d by d e c a r b o n y l a t i o n , no e v i d e n c e o f

t r i c a r b o n y l f o r m a t i o n b e i n g f o u n d . C o p o l y m e r s o f 2 - v i n y l p y r i d i n e

a n d [W( CO) ( 2 - v p ) ] ( 2 0 / 1 m o l e r a t i o ) f o r m t h e c i s - d i s u b s t i t u t e d5

t e t r a c a r b o n y l a t o v e r 100°C, b u t no t r i c a r b o n y l f o r m a t i o n was

112

o b s e r v e d . F o r t h o s e p o l y m e r s o f l o w e r l o a d i n g o f f r e e

2 - v i n y l p y r i d i n e n o t e t r a c a r b o n y l f o r m a t i o n was n o t e d . The

o b s e r v e d r e a c t i o n s o f t h e s e m a t e r i a l s i s i n s h a r p c o n t r a s t t o

t h e o b s e r v e d t h e r m a l r e a c t i o n r o u t e s a v a i l a b l e t o s i m i l a r

p o l y m e r s o f 4 - v i n y l p y r i d i n e . B o t h c o n t a i n a t u n g s t e n

p e n t a c a r b o n y l m o i e t y b o u n d v i a a n i t r o g e n l i g a n d , a n d w e r e

p r e p a r e d b y t h e s ame p r o c e d u r e s . The d i f f e r e n c e i n t h e r m a l

b e h a v i o u r b e t w e e n c o p o l y m e r s o f 4 - v i n y l p y r i d i n e a n d

2 - v i n y l p y r i d i n e m u s t b e a r e s u l t o f s t e r i c h i n d r a n c e t o

c o o r d i n a t i o n i n 2 - v i n y l p y r i d i n e s y s t e m s .

F u r t h e r p o l y m e r s w e r e p r e p a r e d o f s t y r e n e a n d

[W( CO) ( 4 - v i n y l - 4 1- m e t h y l - 2 , 2 ' - b i p y ) ] i n c o r p o r a t i n g e x c e s s4

4 - v i n y l p y r i d i n e . H e a t i n g a p o l y m e r w i t h a 1 / 3 0 m o l e r a t i o o f

4 - v p / s t y r e n e , o r h i g h e r , y i e l d e d b a n d s a t 1888 a n d 1775 cm-1

( s e e F i g u r e 3 . 3 . 2 ) . T h e s e b a n d p o s i t i o n s a r e c l o s e t o t h o s e o f

f a c - [ W ( C O ) 3 ( b i p y ) ( p y ) ] ( 1 8 9 2 a n d 1 77 3 cm” 1 i n n u j o l m u l l )

p r e v i o u s l y r e p o r t e d 9 4 . I t i s t h e r e f o r e p r o p o s e d t h a t t h e

c a r b o n y l c o n t a i n i n g p r o d u c t o b s e r v e d h e r e i s t h e f a c - t r i c a r b o n y l

s p e c i e s . H e a t i n g f u r t h e r l e a d s t o c o m p l e t e d e c a r b o n y l a t i o n

( Scheme 3 . 3 ) .

T h e s e f i n d i n g s s u g g e s t t h a t t h e l o s s o f a CO l i g a n d i s a n

i m p o r t a n t r o u t e f o r t h e t h e r m a l r e a c t i o n s o f t h e s e s y s t e m s i n

t h e a b s e n c e o f e x c e s s b i n d i n g s i t e s . The c o n c e n t r a t i o n o f

p e n d a n t s i t e s on t h e b a c k b o n e i s a l s o i m p o r t a n t i n t h e s e

r e a c t i o n s .

113

F i g . 3 . 3 . 1 C h a n g e s o b s e r v e d i n t h e c a r b o n y l s t r e t c h i n g f r e q u e n c y

r e g i o n o f t h e i n f r a r e d on h e a t i n g a p o l y m e r o f s t y r e n e a nd [W(CO) ( 4 - v p ) ] ( 2 0 / 1 m o l e r a t i o ) c o n t a i n i n g e x c e s s

54 - v i n y l p y r i d i n e b i n d i n g s i t e s ( 5 / 1 m o l e r a t i o o f s t y r e n e t o f r e e

4 - v i n y l p y r i d i n e ) .

22M 2100 20 <30 1900 1000 1700

wavenumbers (cm"1)

I n t h e p r e s e n c e o f e x c e s s binding s i t e s , t h e f a c - t r i c a r b o n y l

species is f o r m e d , a = 20°C, b = 135°C, c = 175°C.

114

F i g . 3 . 3 . 2 C h a n g e s o b s e r v e d i n t h e i n f r a r e d s p e c t r u m ( 2 2 0 0 - 1 7 0 0 cm- 1 ) u p o n h e a t i n g a t e r p o l y m e r o f s t y r e n e a n d [W(CO) ( 4 - v i n y l - 4 ’ - m e t h y l - 2 , 2 ' - b i p y ) ] ( 2 0 / 1 m o l e r a t i o ) w i t h

44 - v i n y l p y r i d i n e ( 1 0 / 1 m o l e r a t i o o f s t y r e n e / 4 - v p ) . T h e s e c h a n g e s

a r e c o n s i s t e n t w i t h t h e f o r m a t i o n o f f a c - t r i c a r b o n y l c o m p l e x .

Wavenumbers

116

Scheme 3 . 3 The e f f e c t o f f r e e b i n d i n g s i t e s on t h e o b s e r v e d

t h e r m a l c h e m i s t r y o f a c o p o l y m e r o f s t y r e n e a n d

[W(CO) ( 4 - v i n y l - 4 ' - m e t h y l - 2 , 2 ' - b i p y ) ] . In t h e p r e s e n c e of4

a d d i t i o n a l b i n d i n g s i t e s t h e f a c - t r i c a r b o n y l s p e c i e s i s f o r m e d .

117

3 . 3 . 3 Effect of Metal Loading

A s e r i e s o f c o p o l y m e r s o f d i f f e r e n t m e t a l l o a d i n g w e r e

p r e p a r e d . At l o a d i n g s on s t y r e n e t o [W(CO) ( 4 - v p ) ] o f g r e a t e r

t h a n 5 : 1 t h e p o l y m e r s b e c o m e i n s o l u b l e . The p o l y m e r s w e r e h e a t e d

a s b e f o r e a n d t h e c h a n g e s i n t h e c a r b o n y l s t r e t c h i n g f r e q u e n c y

r a n g e m o n i t o r e d . At h i g h e r l o a d i n g s t h e m e t a l t e t r a c a r b o n y l

s p e c i e s was p r o d u c e d u n t i l a t l o a d i n g s o f 1 : 6 0 0 a n d l o w e r , no

t e t r a c a r b o n y l s p e c i e s was o b s e r v e d . The a m o u n t o f t h e r m a l l y

p r o d u c e d c i s - t e t r a c a r b o n y l d e c r e a s e d a s t h e l o a d i n g o f t h e m e t a l

c a r b o n y l s p e c i e s i n t h e p o l y m e r was d e c r e a s e d . F i g u r e 3 . 3 . 3

s ho ws t h e c h a n g e i n t h e r a t i o o f t h e p e r c e n t t r a n s m i s s i o n o f

t e t r a c a r b o n y l s p e c i e s ( m e a s u r e d a t t h e h i g h f r e q u e n c y a b s o r p t i o n

a t 2000 cm ) t o p e n t a c a r b o n y 1 ( m e a s u r e d a t 2068 cm" ) w i t h m e t a l

l o a d i n g . No m e t a l t r i c a r b o n y l was f o u n d e v e n a t h i g h e r l o a d i n g s .

F i g . 3 . 3 . 3 P l o t o f t h e r a t i o o f p e r c e n t t r a n s m i s s i o n o f t h e r m a l l y p r o d u c e d m e t a l t e t r a c a r b o n y l t o m e t a l p e n t a c a r b o n y l i n t h e i n f r a r e d f o r c o p o l y m e r s o f s t y r e n e a nd [W(CO) ( 4 - v p ) ] h a v i n g

5d i f f e r e n t m e t a l l o a d i n g s .

Loading

118

T h e s e r e s u l t s s u g g e s t e d t h a t t h e f o r m a t i o n o f t h e

c i s - t e t r a c a r b o n y l s p e c i e s d e p e n d s on t h e p r o x i m i t y o f t h e

p e n t a c a r b o n y l u n i t s on t h e p o l y m e r c h a i n . I t a l s o s u p p o r t s t h e

m e c h a n i s m i n v o l v i n g t h e t h e r m a l c l e a v a g e o f t h e W-N b o n d w i t h

g e n e r a t i o n o f t h e p e n t a c a r b o n y l a n d s u b s e q u e n t r e a c t i o n o f t h i s

f r a g m e n t t o p r o d u c e a t e t r a c a r b o n y 1 c e n t r e a n d m e t a l

h e x a c a r b o n y l , m o r e m e t a l h e x a c a r b o n y l b e i n g d e t e c t e d f o r h i g h e r

1o a d i n g s .

3 . 4 The E f f e c t o f t h e P h y s i c a l P r o p e r t i e s o f t h e P o l y m e r

B a c k b o n e on t h e T h e r m a l C h e m i s t r y

We w e r e i n t e r e s t e d t o i n v e s t i g a t e w h e t h e r p h y s i c a l

p a r a m e t e r s w e r e i m p o r t a n t i n t h e t h e r m a l r e a c t i o n s o f t h e s e

s y s t e m s . The i n f l u e n c e o f t h e m o l a r m a s s a n d g l a s s t r a n s i t i o n

t e m p e r a t u r e (T ) on t h e t h e r m a l c h e m i s t r y w e r e e x a m i n e d u s i n gg

v a r i a b l e t e m p e r a t u r e i n f r a r e d s t u d i e s a n d t h e r m a l m e t h o d s o f

a n a l y s i s . D i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y (DSC) was e m p l o y e d

t o d e t e r m i n e t h e e f f e c t o f m e t a l c a r b o n y l b i n d i n g on t h e p o l y m e r

a n d t o s t u d y t h e i m p o r t a n c e o f t h e Tg on t h e t h e r m a l b e h a v i o u r

o f t h e s e m a t e r i a l s .

3.4.1 Effect of Relative Molar Mass on the Thermal Reactions of

Polymer-Bound W ( C O )^ species.

A s e r i e s o f c o p o l y m e r s o f s t y r e n e a n d 4 - v i n y l p y r i d i n e

( 2 0 / 1 m o l e r a t i o ) o f a r a n g e o f m o l a r m a s s e s

(M = 1 0 , 0 0 0 - 2 0 0 , 0 0 0 a . m . u ) w e r e s y n t h e s i s e d by u s i n g d i f f e r e n t w

a m o u n t s o f t h e i n i t i a t o r a z o b i s i s o b u t y r o n i t r i 1 e ( 0 . 0 5 - 4 % AIBN)

i n t h e p o l y m e r i s a t i o n m i x t u r e . The m o l a r m a s s e s w e r e d e t e r m i n e d

119

by g e l p e r m e a t i o n c h r o m a t o g r a p h y u s i n g p o l y s t y r e n e s t a n d a r d s t o

c o n s t r u c t a c a l i b r a t i o n c u r v e o v e r t h e e x p e c t e d m o l e c u l a r w e i g h t

r a n g e . E a c h o f t h e s e c o p o l y m e r s w e r e t h e n r e a c t e d w i t h

[W(CO) ( T H F ) ] , p r o d u c e d by t h e p h o t o l y s i s o f t h e p a r e n t5

h e x a c a r b o n y l i n THF. S u f f i c i e n t [W(CO) ( THF ) ] was a d d e d t o5

e n s u r e t h a t e v e r y v i n y l p y r i d i n e was c o o r d i n a t e d t o a W(CO)5

u n i t . E x a m i n a t i o n o f t h e s p e c t r a l c h a n g e s o b s e r v e d on h e a t i n g

t h e s e c o p o l y m e r s i n d i c a t e d t h a t t h e same t h e r m a l r e a c t i o n was

o c c u r r i n g f o r a l l t h e p o l y m e r s , i . e . , i n i t i a l d e c a r b o n y l a t i o n o f

t h e W(CO) m o i e t y t o p r o d u c e t h e M(CO) u n i t f o l l o w e d by5 4

c o m p l e t e d e c a r b o n y l a t i o n o f t h e m e t a l c e n t r e s . The T 1s o f t h e s eyp o l y m e r s w e r e d e t e r m i n e d a n d a r e g i v e n i n T a b l e 3 . 4 . 1 t o g e t h e r

w i t h t h e m o l a r m a ss d a t a o f t h e c o p o l y m e r s .

T a b l e 3 . 4 . 1 M o l a r m a s s e s a n d g l a s s t r a n s i t i o n t e m p e r a t u r e s o f c o p o l y m e r s o f s t y r e n e a n d 4 - v i n y l p y r i d i n e p r e p a r e d u s i n g v a r y i n g

a m o u n t s o f AIBN.

% AIBN Tg

( ° c )

M w

( a . m . u )

M n

(a.m.u)

M /M w' n

4. 00 108 10600 5650 1 . 8 82 . 0 0 113 17200 8180 2 . 1 11 . 0 0 120 26500 14880 1 .7 80 . 66 122 38200 19150 2 . 0 00 .5 0 115 47400 28200 1 . 8 80 .4 0 122 51100 25800 1. 980 .3 3 126 67500 30100 2 . 240 . 25 122 70900 31400 2 .2 50 . 2 0 125 99800 47200 2 . 1 10 . 1 0 128 162000 70200 2 .3 10 . 0 5 132 204000 86700 2 . 36

120

The T v a l u e s show t h e e x p e c t e d s l i g h t d e p e n d e n c e ong

r e l a t i v e m o l a r m a s s , i n c r e a s i n g f r o m 108°C t o 132°C f o r a o f

1 0 , 6 0 0 t o 2 0 4 , 0 0 0 a . m . u . A t y p i c a l DSC t h e r m o g r a m o f o ne o f

t h e s e c o p o l y m e r s i s s hown i n F i g u r e 3 . 4 . 1 . The Tg i s t a k e n a s

t h e o n s e t t e m p e r a t u r e o f t h e h e a t c a p a c i t y c h a n g e . A DSC

t h e r m o g r a m o f t h e c o r r e s p o n d i n g m e t a l c a r b o n y l c o n t a i n i n g

p o l y m e r i s i l l u s t r a t e d i n F i g u r e 3 . 4 . 2 . The l a t t e r t h e r m o g r a m i s

d o m i n a t e d by a l a r g e e x o t h e r m i c e v e n t r e p r e s e n t i n g f o r m a t i o n o f

t e t r a c a r b o n y l s p e c i e s , f o l l o w e d b y c o m p l e t e d e c a r b o n y l a t i o n

( v i d e i n f r a ) . S i m i l a r e x o t h e r m s h a v e b e e n r e p o r t e d p r e v i o u s l y i n5 6 95DSC s t u d i e s o f p o l y m e r a n c h o r e d m e t a l c a r b o n y l s ' . The

t h e r m a l r e a c t i o n i s a c c o m p a n i e d by a s h i f t i n b a s e l i n e w h i c h

i m p l i e s a c h a n g e i n e n t r o p y / o r d e r w i t h i n t h e s y s t e m . S i m i l a r

t h e r m o g r a m p r o f i l e s w e r e o b t a i n e d f o r e a c h o f t h e a b o v e

c o p o l y m e r s , a n d f o r t h o s e m e t a l c a r b o n y l c o n t a i n i n g p o l y m e r s o f

2 - v i n y l p y r i d i n e a n d 4 - v i n y l - 4 '- m e t h y l - 2 , 2 '- b i p y r i d y l . From

F i g u r e 3 . 4 . 2 , i t i s a p p a r e n t t h a t t h e i n i t i a l

m o n o d e c a r b o n y l a t i o n o f t h e M(CO) m o i e t y a n d t h e s u b s e q u e n t f u l l5

d e c a r b o n y l a t i o n a r e n o t r e s o l v e d t h e r m a l e v e n t s . I t i s i m p o r t a n t

t o n o t e t h a t i n t h e c a s e o f DSC e x p e r i m e n t s t h e t e m p e r a t u r e i s

c o n t i n u a l l y c h a n g i n g w h i l e i n t h e v a r i a b l e t e m p e r a t u r e i n f r a r e d

e x p e r i m e n t s , t h e t e m p e r a t u r e i s c h a n g e d i n a s t e p - w i s e f a s h i o n .

A f u r t h e r t r a n s i t i o n was o b s e r v e d a t 2 2 0 - 2 8 0 ° C ( d e p e n d i n g

on t h e p o l y m e r ) w h i c h may b e t h e Tg o f t h e p o l y m e r w h i c h now

c o n t a i n s f u l l y d e c a r b o n y l a t e d m e t a l s p e c i e s . T h e r m o g r a v i m e t r i c

a n a l y s i s (TGA) o f t h i s p r o c e s s c o n f i r m e d t h a t w e i g h t l o s s

121

( c a u s e d by s u b l i m a t i o n o f W(CO) o r l o s s o f CO) o c c u r r e d o n l y6

d u r i n g t h e l ow t e m p e r a t u r e e v e n t ( s e e F i g u r e 3 . 4 . 3 ) . T h i s c o u l d

c o n f i r m t h e a s s i g n m e n t o f t h e e v e n t f o l l o w i n g d e c a r b o n y l a t i o n ,

t o a g l a s s t r a n s i t i o n . I t a l s o i n d i c a t e s t h a t a p p r e c i a b l e m e t a l

m u s t r e m a i n w i t h i n t h e p o l y m e r f o l l o w i n g c o m p l e t e

d e c a r b o n y l a t i o n , a s i n a l l p o l y m e r s y s t e m s s t u d i e d w e i g h t l o s s e s

i n t h e r e g i o n 2-5% w e r e f o u n d . ( I f a c o p o l y m e r o f s t y r e n e a n d

[W(CO)s ( 4 - v p ) ] ( 2 0 / 1 m o l e r a t i o ) s u f f e r e d l o s s o f a l l i t ' s m e t a l

a n d CO, a w e i g h t l o s s o f 13% w o u l d b e e x p e c t e d ) . As a

c o n s e q u e n c e , m e t a l l o s s v i a m e t a l h e x a c a r b o n y l f o r m a t i o n m u s t

o n l y b e a m i n o r r o u t e t o t h e l o s s o f t h e c a r b o n y l m o i e t i e s . One

m i g h t e x p e c t t h e g l a s s t r a n s i t i o n t e m p e r a t u r e o f t h e p o l y m e r t o

i n c r e a s e b e c a u s e o f t h e i n c r e a s e i n e n e r g y r e q u i r e d f o r r o t a t i o n

on a t t a c h m e n t o f t h e m e t a l c a r b o n y l f r a g m e n t 76b . An i n c r e a s e i n

t h e T g ' s o f c o p o l y m e r s on b i n d i n g m e t a l c a r b o n y l c o m p l e x e s h a v e

p r e v i o u s l y b e e n r e p o r t e d i n s t u d i e s o f b o u n d i r o n c a r b o n y l

9 5c o m p l e x e s , a n d i n t h e r m a l s t u d i e s o f p o l y s t y r e n e a n c h o r e dq c

c h r o m i u m t r i c a r b o n y l . A t t e m p t s t o o b t a i n t h e Tg o f t h e

d e c a r b o n y l a t e d p o l y m e r , p r o v e d t o b e u n s u c c e s s f u l .

T h e s e r e s u l t s c o n f i r m t h a t t h e m o l a r m a s s o f t h e p o l y m e r

b a c k b o n e h a s l i t t l e i n f l u e n c e on t h e d i r e c t i o n o f r e a c t i o n s o f

t h e m e t a l p e n t a c a r b o n y l s b o u n d t o t h e p o l y m e r . H o w e v e r , t h e

p h y s i c a l p r o p e r t i e s o f t h e p o l y m e r a r e s i g n i f i c a n t l y a f f e c t e d by

t h e p r e s e n c e o f t h e p e n t a c a r b o n y l m o i e t i e s a s i n d i c a t e d by t h e

a p p e a r a n c e o f a new g l a s s t r a n s i t i o n t e m p e r a t u r e a t a h i g h e r

t e m p e r a t u r e t h a n t h e T o f t h e n o n - m e t a l 1a t e d p o l y m e r .y

122

F i g . 3 . 4 . 1 DSC t h e r m o g r a m o f a c o p o l y m e r o f s t y r e n e a n d 4 - v i n y l -

p y r i d i n e (Mw = 1 0 , 6 0 0 a . m . u ) . ( T g o n s e t = 1 1 0 ° C ; H e a t i n g r a t e =

5 ° C / m i n , A t m o s p h e r e = Nz a t 30 cm3/ m i n ) .

Temperature (*C)

F i g . 3 . 4 . 2 DSC t h e r m o g r a m o f a c o p o l y m e r o f s t y r e n e a n d

[W(CO) ( 4 - v p ) ] . ( H e a t i n g r a t e := 5 ° C / m i n ; A t m o s p h e r e = N a t5 2

30 cm3/ m i n ) .

Temperature ('C)

123

F i g . 3 . 4 . 3 TGA c u r v e f o r a c o p o l y m e r o f s t y r e n e a n d

[W( CO) ( 4 - v p ) ] . A 4% w e i g h t l o s s o c c u r s b e t w e e n 1 1 0 - 1 6 5 ° C , w i t h5

d e c o m p o s i t i o n a t 330°C. ( H e a t i n g r a t e = 1 0 ° C / m i n ; A t m o s p h e r e =

N a t 10 cm3/ m i n ) .2

% Weight Loss

Temperature (*C)

3 . 4 . 2 The I m p o r t a n c e o f t h e Glass T r a n s i t i o n T e m p e r a t u r e .

I n t h e DSC s t u d i e s o f t h e s e p o l y m e r - b o u n d m a t e r i a l s t h e

d e c a r b o n y l a t i o n r e a c t i o n s commenced a t a t e m p e r a t u r e c l o s e t o

t h e T o f t h e u n m e t a l l a t e d p o l y m e r . T h i s o b s e r v a t i o n p o s e d t h e

q u e s t i o n a s t o w h e t h e r o r n o t t h e e x t r a c h a i n m o b i l i t y i n d u c e d

by e x c e e d i n g t h e g l a s s t r a n s i t i o n o f t h e p o l y m e r was a

p r e r e q u i s i t e f o r t h e t h e r m a l r e a c t i o n s t o o c c u r .

I n o r d e r t o i n v e s t i g a t e t h e i m p o r t a n c e o f t h e Tg on t h e

o b s e r v e d t h e r m a l r e a c t i o n s , a s e r i e s o f c o p o l y m e r s o f

4 - v i n y l p y r i d i n e a n d v a r i o u s c omo n o me rs w e r e s y n t h e s i s e d . T h e s e

124

c om o no m e r s w e r e e t h y l a n d m e t h y l a c r y l a t e a n d « - m e t h y l s t y r e n e

a n d w e r e c h o s e n b e c a u s e t h e i r p o l y m e r s e x h i b i t a w i d e T r a n g ey( l i t e r a t u r e v a l u e s f o r h o m o p o l y m e r s : p o l y e t h y l a c r y l a t e = - 2 4 ° C ,

p o l y m e t h y l a c r y l a t e = 0°C a n d p o l y - a - m e t h y l s t y r e n e = 1 7 2 ° C ) 7 6 .

H o w e v e r , a l t e r a t i o n s i n t h e c h e m i s t r y o f t h e c omonomer w o u l d

o b v i o u s l y r e s u l t i n c o p o l y m e r s o f v a s t l y d i f f e r i n g c h e m i c a l

p r o p e r t i e s w h i c h i n t h e m s e l v e s may e f f e c t t h e t h e r m a l r e a c t i o n s

o f t h e b o u n d m e t a l c a r b o n y l s . F o r t h i s r e a s o n , c o p o l y m e r s o f

4 - v i n y l p y r i d i n e a n d m e t h y l m e t h a c r y l a t e w e r e p r e p a r e d . T h e s e

c o p o l y m e r s h a v e a Tg ( o n s e t 110°C) s i m i l a r t o c o p o l y m e r s o f

s t y r e n e a n d 4 - v i n y l p y r i d i n e , w h i l e t h e c h e m i s t r y o f t h e p o l y m e r

b a c k b o n e s h o u l d r e s e m b l e t h a t o f t h e

4 - v i n y l p y r i d i n e - c o - e t h y l a c r y l a t e c o p o l y m e r ( t h e o n l y d i f f e r e n c e

b e i n g t h e p r e s e n c e o f a n « _ CH3 i n m e t h y l m e t h a c r y l a t e p o l y m e r s ) .

The T g ' s o f c o p o l y m e r s o f 4 - v i n y l p y r i d i n e w i t h m e t h y l a n d

e t h y l a c r y l a t e w e r e d e t e r m i n e d t o b e - 2 2 ° C a n d +9°C

r e s p e c t i v e l y . T h e s e m a t e r i a l s w e r e i s o l a t e d a s r u b b e r y s o l i d s a s

o p p o s e d t o t h o s e p o l y m e r s o f s t y r e n e a n d m e t h y l m e t h a c r y l a t e o f

h i g h e r T ' s w h i c h w e r e o b t a i n e d a s p o w d e r s . M e t a l c a r b o n y l yc o n t a i n i n g c o p o l y m e r s ( 2 0 / 1 m o l e r a t i o ) o f e t h y l a n d m e t h y l

a c r y l a t e w e r e p r e p a r e d by c o p o l y m e r i s a t i o n o f t h e a c r y l a t e w i t h

[W(CO) ( 4 - v p ) ] . The r e s u l t i n g p o l y m e r o f e t h y l a c r y l a t e was

i s o l a t e d a s a r u b b e r y s o l i d (T < room t e m p e r a t u r e ) w h i l e t h a t

o f m e t h y l a c r y l a t e was a p o w d e r (T > room t e m p e r a t u r e ) . H e a t i n ggt h e s e p o l y m e r s i n t h e v a r i a b l e t e m p e r a t u r e c e l l r e s u l t e d i n

c h a n g e s i n t h e i n f r a r e d s i m i l a r t o t h o s e o f m e t a l l a t e d

125

c o p o l y m e r s o f m e t h y l m e t h a c r y l a t e a n d s t y r e n e , i . e . ,

c i s - t e t r a c a r b o n y l f o r m a t i o n f o l l o w e d by d e c a r b o n y l a t i o n .

E x a m i n i n g t h e DSC t r a c e o f t h e s e a c r y l a t e c o p o l y m e r s ( s e e

F i g u r e 3 . 4 . 5 ) i t i s a p p a r e n t t h a t t h e d e c a r b o n y l a t i o n e v e n t i s

n o t w e l l d e f i n e d . The b a s e l i n e s l o p e s g r a d u a l l y u n t i l a t a b o u t

110°C a s h o u l d e r e d e x o t h e r m i c e v e n t o c c u r s . The s l o p i n g

b a s e l i n e , w h i c h i s a b s e n t i n t h e DSC o f t h e n o n - m e t a l 1a t e d

c o p o l y m e r ( F i g u r e 3 . 4 . 4 ) , s u g g e s t e d t h a t t h e t h e r m a l r e a c t i o n

may b e t a k i n g p l a c e a f t e r t h e g l a s s t r a n s i t i o n t e m p e r a t u r e h a d

b e e n r e a c h e d . I n d e e d , F i g u r e 3 . 4 . 5 s h o w s t h e s p e c t r a o b t a i n e d

a f t e r m a i n t a i n i n g a f i l m o f a c o p o l y m e r o f e t h y l a c r y l a t e a n d

[W( CO) ( 4 - v p ) ] a t 70°C a n d c o n t i n u o u s l y s c a n n i n g t h e c a r b o n y l5

s t r e t c h i n g f r e q u e n c y r e g i o n o f t h e i n f r a r e d a t f i x e d t i m e

i n t e r v a l s . The r e s u l t was a g r a d u a l b u t s t e a d y d e c r e a s e i n

i n t e n s i t y o f t h e p e n t a c a r b o n y l c a r b o n y l b a n d s w i t h c o n c o m i t a n t

f o r m a t i o n o f b a n d s w h i c h c a n b e a s s i g n e d t o t h e t e t r a c a r b o n y l

s p e c i e s , f o l l o w e d e v e n t u a l l y by t o t a l d e c a r b o n y l a t i o n . A s i m i l a r

r e s u l t was f o u n d f o r m e t h y l a c r y l a t e c o p o l y m e r s c o n t a i n i n g b o u n d

m e t a l p e n t a c a r b o n y l o r t e t r a c a r b o n y l . F o r t h o s e c o p o l y m e r s o f

s t y r e n e a n d m e t h y l m e t h a c r y l a t e o f h i g h e r g l a s s t r a n s i t i o n

t e m p e r a t u r e s , no c h a n g e i n t h e i n t e n s i t y o f t h e c a r b o n y l

s t r e t c h i n g f r e q u e n c i e s was f o u n d on p r o l o n g e d h e a t i n g a t 70°C.

The f a c t t h a t a c o p o l y m e r o f m e t h y l m e t h a c r y l a t e u n d e r g o e s no

r e a c t i o n a t 70°C r u l e s o u t t h e p o s s i b i l i t y o f o x y g e n d o n o r s i t e s

a c t i n g a s b i n d i n g s i t e s . R e a c t i o n o f t h e a c r y l a t e was f o u n d t o

p r o c e e d a t l o w e r t e m p e r a t u r e s (50°C) b u t a t s l o w e r r a t e s .

126

t h r e s h o l d t e m p e r a t u r e t h e r e a c t i o n w i l l p r o c e e d a b o v e t h e Tg o f

t h e p o l y m e r , a n d i f t h e T i s a b o v e t h e t h r e s h o l d t e m p e r a t u r eyt h e r e a c t i o n p r o c e e d s a t t h i s t h r e s h o l d t e m p e r a t u r e .

temperature reaction proceeds anyway. If the is below the

F i g . 3 . 4 . 4 DSC t h e r m o g r a m o f a c o p o l y m e r o f e t h y l a c r y l a t e a nd 4 - v i n y l p y r i d i n e ( 2 0 / 1 m o l e r a t i o ) . (T = - 2 2 ° C , H e a t i n g r a t e =

5 ° C / m i n , A t m o s p h e r e = N2 a t 30 cm3/ m i n ) .

j 0 0 P © r Q t u r e (* 0 )

F i g . 3 . 4 . 4 DSC t h e r m o g r a m o f a c o p o l y m e r o f e t h y l a c r y l a t e a n d

[W(CO) ( 4 - v p ) ] . ( H e a t i n g r a t e = 5 ° C / m i n , A t m o s p h e r e = N a t5 2

30 cm3/ m i n ) .

Temperature (*C)

128

F i g . 3 . 4 . 5 a C h a n g e s o b s e r v e d i n t h e 2 2 0 0 - 1 7 0 0 cm"1 r e g i o n o f t h e

i n f r a r e d on h e a t i n g a c o p o l y m e r o f e t h y l a c r y l a t e a n d

[W(CO) ( 4 - v p ) ] t o 70°C f o r 1 6 h .5

22ee 2ioe 2009 1900 leee I7ee

wavenumbers ( cm- 1 )

On c o n t i n u e d h e a t i n g , m a i n t a i n i n g t h e t e m p e r a t u r e a t 70°C, the

p e n t a c a r b o n y l b a n d s d e c r e a s e i n i n t e n s i t y a n d a r e r e p l a c e d b y t h o s e o f t h e c i s -disubsti t u t e d tetracarbonyl bands.

The band at 1727 cm ^ i s d u e t o t h e acrylate backbone.

129

F i g . 3 . 4 . 5 b C h a n g e s o b s e r v e d i n t h e c a r b o n y l s t r e t c h i n g

f r e q u e n c y r e g i o n o f t h e i n f r a r e d on c o n t i n u e d h e a t i n g o f a

c o p o l y m e r o f e t h y l a c r y l a t e a n d [W(CO) ( 4 - v p ) ] f o r 3 0 h .5

2200 2iu0 2000 1900 IQ0O 1709

wavenumbers ( c m ' 1)

Continued heating at 70°C results in e v e n t u a l decarbonylation . No such reaction occurs for polymers of s t y r e n e o r

m e t h y I m e t h a c r y l a t e .

130

Much o f t h e i n t e r e s t i n t h e t h e r m a l c h e m i s t r y o f m e t a l

c a r b o n y l s when b o u n d t o o r g a n i c p o l y m e r s u p p o r t s h a s b e e n

c o n c e r n e d w i t h t h e f o r m a t i o n o f c o l l o i d a l m e t a l d i s p e r s i o n s

w i t h i n p o l y m e r m a t r i c e s . Many o f t h e s t u d i e s h a v e b e e n p e r f o r m e d

by p r e p a r i n g h o m o g e n e o u s s o l u t i o n s o f m e t a l c a r b o n y l s a n d t h e

p o l y m e r m a t r i x a n d s u b s e q u e n t g e n e r a t i o n o f t h e m e t a l o r m e t a l

o x i d e d o m a i n s by t h e r m a l , p h o t o l y t i c o r e l e c t r o n beam

m e t h o d s 88' 9 0 . O t h e r r e p o r t s h a v e d e a l t w i t h t h e t h e r m a l

d e c o m p o s i t i o n o f a n c h o r e d m e t a l c a r b o n y l s y s t e m s i n

s o l u t i o n 62' 63' 95' 9 6 . I t s e e m e d l i k e l y t h a t h e a t i n g c a s t f i l m s o f

p o l y m e r a t t a c h e d g r o u p 6 m e t a l c a r b o n y l s may a f f o r d p o l y m e r s

c o n t a i n i n g s m a l l m e t a l c l u s t e r s h a v i n g c a t a l y t i c a c t i v i t y .

E a c h o f t h e t h e r m a l r e a c t i o n s o f a l l t h e s t u d i e d p o l y m e r

s y s t e m s p r o d u c e d f u l l y d e c a r b o n y l a t e d m e t a l c e n t r e s ( v i d e

i n f r a r e d s p e c t r o s c o p y ) u n d e r r e l a t i v e l y m i l d t h e r m a l c o n d i t i o n s .

The m e c h a n i s m s u g g e s t e d was o n e o f a d i s s o c i a t i v e p r o c e s s

i n v o l v i n g t h e f o r m a t i o n o f f r e e m e t a l p e n t a c a r b o n y 1 f r a g m e n t s

w h i c h r e a c t w i t h o t h e r b o u n d p e n t a c a r b o n y 1 u n i t s p r o d u c i n g t h e

t e t r a c a r b o n y l c e n t r e a n d m e t a l h e x a c a r b o n y l ( i n t h e c a s e o f

p o l y m e r s o f [M(CO) ( 4 - v p ) ] ) . T h e p r o d u c t i o n o f m e t a l5

h e x a c a r b o n y l was c o n f i r m e d by a n a l y s i s o f t h e p r o d u c t s i n t h e

h e a d s p a c e a b o v e a h e a t e d s a m p l e . T h i s p r o c e s s w o u l d r e s u l t i n

a p p r e c i a b l e m e t a l l o s s b e c a u s e o f s u b l i m a t i o n o f t h e

h e x a c a r b o n y l f r o m t h e p o l y m e r . T h e r m o g r a v i m e t r i c a n a l y s i s o f t h e

p o l y m e r s h o w e v e r , r e v e a l e d t h a t l i t t l e m e t a l was l o s t u p o n

3.5 Analysis of the Thermal Product of the Decarbonyl ation.

131

d e c a r b o n y l a t i o n . A mo r e q u a n t i t a t i v e e v a l u a t i o n o f t h e m e t a l

c o n t e n t f o l l o w i n g t h e r m a l r e a c t i o n was r e q u i r e d .

The a m o un t o f m e t a l r e m a i n i n g f o l l o w i n g d e c a r b o n y l a t i o n was

d e t e r m i n e d by a t o m i c a b s o r p t i o n s p e c t r o s c o p y . One s e t o f

p o l y m e r s w e r e t h e r m a l l y r e a c t e d u n d e r v a c u u m a t 200°C. The

a b s e n c e o f c a r b o n y l s t r e t c h i n g f r e q u e n c i e s i n t h e r e a c t e d

s a m p l e s was c o n f i r m e d by i n f r a r e d s p e c t r o s c o p y . T h e s e s a m p l e s

w e r e a n a l y s e d f o r m e t a l c o n t e n t a n d c o m p a r e d w i t h a s e t o f

i d e n t i c a l u n r e a c t e d s a m p l e s . R e s u l t s s h o w e d t h a t a s much a s 90%

o f t h e m e t a l r e m a i n e d w i t h i n t h e p o l y m e r m a t r i x f o l l o w i n g

t h e r m a l r e a c t i o n . Of a l l t h e p o l y m e r s s t u d i e d t h e r e w e r e no

s i g n i f i c a n t d i f f e r e n c e s i n t h e p e r c e n t a g e m e t a l r e m a i n i n g ,

r e g a r d l e s s o f t h e p o l y m e r c o m p o s i t i o n .

A n a l y s i s o f d e c a r b o n y l a t e d p o l y m e r f i l m s o f s t y r e n e a nd

[M(CO) ( 4 - v p ) ] by X - r a y p h o t o e l e c t r o n s p e c t r o s c o p y ( X P S ) 97 ,5

r e v e a l e d t h e p r e s e n c e o f WO^ d i s p e r s i o n s on t h e s u r f a c e o f t h e

f i l m s . D e c a r b o n y l a t i o n s w e r e c a r r i e d o u t u n d e r v a c u u m , s o

p r e s u m a b l y h i g h l y r e a c t i v e e l e m e n t a l m e t a l l i c s p e c i e s p r o d u c e d

r e a c t w i t h o x y g e n t o f o r m t h e m e t a l o x i d e on e x p o s u r e t o a i r .

T h i s wo r k s u g g e s t s t h a t h i g h c o n c e n t r a t i o n s o f m e t a l o r

m e t a l o x i d e d i s p e r s i o n s c a n b e p r o d u c e d u n d e r m i l d c o n d i t i o n s

( l e s s t h a n 70°C f o r e t h y l a c r y l a t e c o p o l y m e r s ) . I t i s a l s o v e r y

l i k e l y t h a t m e t a l l i c c h r o m i u m a n d m o l y b d e n u m d i s p e r s i o n s a r e

p r o d u c e d on t h e r m a l d e c o m p o s i t i o n o f p o l y m e r s when M = Cr o r Mo.

132

F u r t h e r s t u d i e s o f t h e s e m a t e r i a l s a r e n e c e s s a r y t o i n v e s t i g a t e

a s p e c t s o f n u c l é a t i o n a n d g r o w t h o f m e t a l a n d m e t a l o x i d e

c l u s t e r s i n t h e s o l i d s t a t e a s w e l l a s t h e p r o p e r t i e s o f s u c h

m i c r o p a r t i c l e s a s a f u n c t i o n o f c l u s t e r s i z e , c o n c e n t r a t i o n a n d

e n v i r o n m e n t .

3 . 6 C o n c l u s i o n s

I n v e s t i g a t i o n s o f t h e t h e r m a l p r o p e r t i e s o f t h e s e p o l y m e r s

when c a s t a s f i l m s h a v e s hown t h a t t h e c h e m i s t r y o f m e t a l

c o m p l e x e s b o u n d t o c o p o l y m e r s o f 2 - v i n y l p y r i d i n e d i f f e r s

s i g n i f i c a n t l y f r o m t h a t o f c o p o l y m e r s o f 4 - v i n y l p y r i d i n e . I n t h e

c a s e o f c o p o l y m e r s o f 2 - v i n y l p y r i d i n e l o s s o f t h e m e t a l c a r b o n y l

f r a g m e n t a p p e a r s t o b e t h e o n l y t h e r m a l r o u t e a v a i l a b l e . T h i s i s

p r o b a b l y a r e s u l t o f s i g n i f i c a n t s t e r i c h i n d r a n c e by t h e p o l y m e r

t o t h e c o o r d i n a t i o n o f t h e p y r i d i n e i n t h e s e p o l y m e r s . F o r t h o s e

p o l y m e r s o f 4 - v i n y l p y r i d i n e , t h e t h e r m a l c h e m i s t r y i n v o l v e s t h e

f o r m a t i o n o f t h e c i s - d i s u b s t i t u t e d t e t r a c a r b o n y l c o m p l e x . T h i s

i s i n s h a r p c o n t r a s t t o t h a t o f m o n o m e r i c [W(CO) ( p y r i d i n e ) ] ,5

w h i c h s u b l i m e s on h e a t i n g . P o l y m e r s c o n t a i n i n g 2 , 2 ' - b i p y r i d y l

m e t a l t e t r a c a r b o n y l c o m p l e x e s s u f f e r e d t h e l o s s o f t h e c a r b o n y l

s t r e t c h i n g f r e q u e n c i e s a t e l e v a t e d t e m p e r a t u r e s . I n t h e p r e s e n c e

o f f r e e b i n d i n g s i t e s on t h e p o l y m e r b a c k b o n e , t h e

f a c - t r i c a r b o n y l s p e c i e s i s f o r m e d . P o l y m e r s o f e t h y l a n d m e t h y l

a c r y l a t e w e r e f o u n d t o u n d e r g o t h e r m a l d e c a r b o n y l a t i o n s a t l o w e r

t e m p e r a t u r e s t h a n t h o s e c o p o l y m e r s o f s t y r e n e ,

m e t h y l m e t h a c r y l a t e , a nd a - m e t h y l s t y r e n e . T h i s d i f f e r e n c e was

a t t r i b u t e d t o a d i f f e r e n c e i n g l a s s t r a n s i t i o n t e m p e r a t u r e s . The

133

l o w e r T o f t h e a c r y l a t e p o l y m e r s l o w e r e d t h e r e a c t i o n 9

t e m p e r a t u r e b e c a u s e o f t h e i n c r e a s e d p o l y m e r c h a i n m o b i l i t y a t

t e m p e r a t u r e s a b o v e t h e T .

S t u d i e s o f c o p o l y m e r s o f s t y r e n e c o n t a i n i n g b o u n d

[W(CO)s ( 4 - v p ) ] u n i t s , s u g g e s t e d t h a t a d i s s o c i a t i v e m e c h a n i s m

i n v o l v i n g t h e f o r m a t i o n o f f r e e p e n t a c a r b o n y l f r a g m e n t s was

t a k i n g p l a c e on h e a t i n g t h e s e p o l y m e r s . T h e s e h i g h l y r e a c t i v e

c o o r d i n a t i v e l y u n s a t u r a t e d s p e c i e s c o u l d b e s t a b i l i s e d by o l e f i n

i n t e r a c t i o n s w i t h t h e p o l y m e r b a c k b o n e . The m e c h a n i s m p r o p o s e d

s u g g e s t e d t h a t r e a c t i o n o f t h e s e f r a g m e n t s w i t h b o u n d

p e n t a c a r b o n y l u n i t s p r o d u c e s a c i s - t e t r a c a r b o n y l c e n t r e a n d

m e t a l h e x a c a r b o n y l . The t e t r a c a r b o n y l c e n t r e w o u l d t h e n

c o o r d i n a t e t o t h e p y r i d i n e s i t e on t h e p o l y m e r f o r m e d b y t h e

c l e a v a g e o f (CO) W-N b o n d p r o d u c i n g a m e t a l t e t r a c a r b o n y l5

s p e c i e s b o u n d t h r o u g h two p y r i d i n e c o o r d i n a t i o n s i t e s on t h e

p o l y m e r b a c k b o n e . A n a l y s i s o f t h e v o l a t i l e s o f t h e r e a c t i o n

s u p p o r t e d t h i s p r o c e s s . H o w e v e r , r e s u l t s f r o m a t o m i c a b s o r p t i o n

s p e c t r o s c o p y (AAS) a n d t h e r m o g r a v i m e t r i c a n a l y s i s (TGA)

e x p e r i m e n t s s h owe d t h a t m o s t o f t h e m e t a l r e m a i n s a f t e r

d e c a r b o n y l a t i o n h a s o c c u r r e d . I t i s t h o u g h t t h e n t h a t t h e a b o v e

m e c h a n i s m i s n o t t h e o n l y o n e ( s e e l a t e r ) . F r om e x p e r i m e n t s w i t h

p o l y m e r s o f d i f f e r e n t m e t a l l o a d i n g s , t h e p r o x i m i t y o f two m e t a l

p e n t a c a r b o n y l m o i e t i e s was f o u n d t o b e i m p o r t a n t f o r t h e o u t c o m e

o f t h e r e a c t i o n . I n t h e p r e s e n c e o f f r e e p e n d a n t s i t e s on t h e

p o l y m e r b a c k b o n e , t h e f a c - t r i c a r b o n y l i s f o r m e d . The

f a c - t r i c a r b o n y l i s a l s o p r o d u c e d on h e a t i n g t e r p o l y m e r s o f

134

[W(CO) ( 4 - v i n y l - 4 ' - m e t h y l - 2 , 2 ' - b i p y r i d y l ) ] i n c o r p o r a t i n g f r e e4

p e n d a n t s i t e s , s u g g e s t i n g t h a t CO d i s s o c i a t i o n i s a n i m p o r t a n t

t h e r m a l r o u t e f o r p o l y m e r a n c h o r e d b i p y r i d y l c a r b o n y l c o m p l e x e s .

No e v i d e n c e o f m e t a l d i c a r b o n y l o r m o n o c a r b o n y l was f o u n d

i n d i c a t i n g t h a t d e c a r b o n y l a t i o n o c c u r s r a p i d l y p a s t t h e

t r i c a r b o n y l s t a g e .

T h e r m o g r a v i m e t r i c a n d a t o m i c a b s o r p t i o n s p e c t r o s c o p y

e x p e r i m e n t s do n o t s u p p o r t t h e a b o v e m e c h a n i s m . F o l l o w i n g

c l e a v a g e o f t h e W — N b o n d a n d t h e p r o d u c t i o n o f t h e m e t a l

h e x a c a r b o n y l , o ne w o u l d e x p e c t a much g r e a t e r m e t a l l o s s

f o l l o w i n g t h e r m a l d e c a r b o n y l a t i o n o f t h e m e t a l c e n t r e s , b e c a u s e

o f s u b l i m a t i o n o f t h e m e t a l h e x a c a r b o n y l . D a t a f r o m TGA a n d AAS

e x p e r i m e n t s i n d i c a t e d t h a t a l m o s t a l l t h e m e t a l r e m a i n e d w i t h i n

t h e p o l y m e r m a t r i x f o l l o w i n g d e c a r b o n y l a t i o n . A l t h o u g h g a s e o u s

m e t a l h e x a c a r b o n y l was d e t e c t e d a s a p r o d u c t o f t h e

d e c a r b o n y l a t i o n , t h e e x t i n c t i o n c o e f f i c i e n t o f g a s e o u s

h e x a c a r b o n y l i n t h e i n f r a r e d i s p r o b a b l y v e r y l a r g e , a n d a s a

r e s u l t t h e m e t a l h e x a c a r b o n y l may o n l y b e a v e r y m i n o r p r o d u c t .

An a l t e r n a t i v e m e c h a n i s m i s t h u s p r o p o s e d . The t h e r m a l r e a c t i o n

o f a c o p o l y m e r o f s t y r e n e a n d [W(CO) ( 4 - v p ) ] may i n v o l v e CO5

d i s s o c i a t i o n t o y i e l d a m e t a l t e t r a c a r b o n y 1 c e n t r e s t a b i l i s e d by

a l k e n e i n t e r a c t i o n s w i t h t h e p o l y m e r b a c k b o n e ( S c h e m e 3 . 4 ) . S u c h

a n i n t e r a c t i o n w o u l d n o t b e e x p e c t e d t o b e s t a b l e i n s o l u t i o n ,

b u t i n t h e s o l i d p o l y m e r m a t r i x t h e m e t a l c e n t r e i s s u r r o u n d e d

by p o t e n t i a l a l k e n i c l i g a n d s a n d s o s u c h a n i n t e r a c t i o n may b e

f a v o u r a b l e . T h e r m a l d i s s o c i a t i o n o f a CO l i g a n d f o r m s a m e t a l

135

w ( c o ) 5

A

5< A

Scheme 3 . 4______________________________________________________________________________

t e t r a c a r b o n y l c e n t r e , w h i c h c o u l d t h e n c o o r d i n a t e a n a l k e n e

g r o u p on t h e p o l y s t y r e n e b a c k b o n e t o p r o d u c e a

[W( CO) ( p y ) (riz - a l k e n e ) ] s p e c i e s . F u r t h e r h e a t i n g r e s u l t s i n4

d e c a r b o n y l a t i o n o f t h e m e t a l c e n t r e a s t h e t r i c a r b o n y l i n v o l v i n g

136

c o o r d i n a t i o n t o two a l k e n e g r o u p s may n o t b e t h e r m a l l y s t a b l e . A

n u m b e r o f a l k e n e c o m p l e x e s o f t h e g e n e r a l f o r m u l a [M(CO) ( L) ]6 - n n

(L = r]2- a l k e n e ) h a v e b e e n r e p o r t e d " . T h e s e h a v e b e e n p r e p a r e d

by e i t h e r h e a t i n g t o g e t h e r M(CO) a n d t h e a p p r o p r i a t e a l k e n e o r6p e r f o r m i n g t h e r e a c t i o n u n d e r UV i r r a d i a t i o n .

I n t h e p r e s e n c e o f e x c e s s p y r i d i n e b i n d i n g s i t e s on t h e

p o l y m e r b a c k b o n e , t h e f a c - [ W ( C 0 ) 3 ( p y ) 2 (r} - a l k e n e ) ] s p e c i e s c o u l d

b e f o r m e d ( S ch eme 3 . 5 ) . The p r e p a r a t i o n o f t h e c o m p l e x e s

c i s - [ W ( C O ) (L) (rj2- a l k e n e ) ] a n d f a c - [ W ( C O ) (L) (rj2- a l k e n e ) ] h a v e4 3 2

oo 4 onb e e n p r e v i o u s l y d e s c r i b e d ' . T h e r e a r e r e l a t i v e l y f e w

2 9 9 1 0 1 •c h r o m i u m rj - a l k e n i c c o m p l e x e s known ' , a n d i n g e n e r a l t h e

9 9s t a b i l i t y o f t h e c o m p l e x e s i s i n t h e o r d e r W > Mo >> Cr . T h i s

g r e a t e r i n s t a b i l i t y o f t h e a l k e n i c c o m p l e x e s o f c h r o m i u m w o u l d

e x p l a i n why no d i s u b s t i t u t e d t e t r a c a r b o n y l s p e c i e s w e r e o b s e r v e d

on h e a t i n g c o p o l y m e r s o f [ Cr (CO) ( 4 - v p ) ] . I n t h e c a s e o f5

c o p o l y m e r s o f m e t h y l o r e t h y l a c r y l a t e a n d m e t h y l m e t h a c r y l a t e ,

o x y g e n s i t e s on t h e p o l y m e r b a c k b o n e c o u l d s t a b i l i s e t h e

t e t r a c a r b o n y l c e n t r e . T h e r e i s no f i r m e x p e r i m e n t a l e v i d e n c e f o r

t h i s m e c h a n i s m , i t i s p u r e l y s p e c u l a t i v e . I t i s t h e m o s t

p l a u s i b l e e x p l a n a t i o n a s s u c h a m e c h a n i s m w o u l d r e s u l t i n a

l a r g e p e r c e n t a g e o f t h e m e t a l r e m a i n i n g w i t h i n t h e p o l y m e r

m a t r i x f o l l o w i n g t h e r m a l d e c a r b o n y l a t i o n o f t h e m e t a l c e n t r e s .

137

C h a i n m o b i l i t y i s i m p o r t a n t i n t h e t h e r m a l c h e m i s t r y o f

t h e s e m a t e r i a l s . A c r y l a t e p o l y m e r s w e r e f o u n d t o u n d e r g o

d e c a r b o n y l a t i o n a t 70°C o r l o w e r , w h i l e t h o s e o f h i g h e r T w e r eg

t h o u g h t t o b e g i n r e a c t i o n a t a t h r e s h o l d t e m p e r a t u r e a r o u n d

138

100°C. C o m p l e t e d e c a r b o n y l a t i o n was a c h i e v e d a t a r o u n d 160°C.

C o m p l e t e d e c a r b o n y l a t i o n w o u l d n o t t a k e p l a c e a t a r o u n d 100°C,

h o w e v e r , i n c o n t r a s t t o p o l y m e r s o f e t h y l a c r y l a t e w h i c h c o u l d

be f u l l y d e c a r b o n y l a t e d a t 70°C. At t h e g l a s s t r a n s i t i o n ,

r o t a t i o n a b o u t s i n g l e b o n d s i s no l o n g e r r e s t r i c t e d a n d t h e

o n s e t o f l a r g e - s c a l e m o t i o n o f c h a i n m o l e c u l a r s e g m e n t s b e g i n s

a n d s o t h e p o l y m e r b e c o m e s m o r e f l u i d . Above t h e T , t h e c h a i ngs e g m e n t s c a n u n d e r g o c o o p e r a t i v e r o t a t i o n a l , t r a n s i t i o n a l , a n d

d i f f u s i o n a l m o t i o n a n d a s t h e t e m p e r a t u r e i s r a i s e d s u f f i c i e n t l y

( t o , s a y Tg +100°C) t h e m a t e r i a l b e h a v e s l i k e a l i q u i d , h a v i n g

o f c o u r s e v e r y h i g h v i s c o s i t y . The a v e r a g e m o b i l i t y o f t h e c h a i n

s e g m e n t s i n c r e a s e s d r a m a t i c a l l y a n d a s a r e s u l t , t h e l i f e t i m e o f

r e a c t i v e s p e c i e s f o r m e d t h e r m a l l y w i l l b e d e c r e a s e d . B e l o w t h e

T , r o t a t i o n a b o u t t h e s i n g l e b o n d s o f t h e p o l y m e r c h a i n i s

r e s t r i c t e d . I n t h e c a s e o f e t h y l a c r y l a t e c o p o l y m e r s , a t 70°C

t h e p o l y m e r i s w e l l a b o v e i t ' s T a n d s o t h e m e t a l c a r b o n y lg

c o m p l e x e s w o u l d h a v e s u f f i c i e n t m o b i l i t y t o a l l o w t e t r a c a r b o n y l

f o r m a t i o n , a n d w o u l d b e e x p e c t e d t o h a v e much g r e a t e r m o b i l i t y

t h a n t h e m e t a l c a r b o n y l c o m p l e x e s i n p o l y m e r s h a v i n g h i g h e r

T g ' s . I n many s t u d i e s o f p o l y m e r - b o u n d o r g a n o m e t a l 1 i c c a t a l y s t s ,

p o l y m e r s o f h i g h c r o s s l i n k d e n s i t i e s h a v e b e e n c o n s t r u c t e d t o

d e c r e a s e m o b i l i t y t o i n c r e a s e t h e l i f e t i m e o f r e a c t i v e s p e c i e s

by p r e v e n t i n g s e l f - a g g r e g a t i o n a f f o r d i n g h i g h c o n c e n t r a t i o n s o f2 o i o 7 4u n s a t u r a t e d c o m p l e x e s ' ' H o w e v e r , t h e f o r m a t i o n o f

u n i f o r m m e t a l d i s p e r s i o n s a t s u c h m i l d c o n d i t i o n s s e e m s a n

a t t r a c t i v e p r o s p e c t .

139

T h e s e e x p e r i m e n t s h a v e d e m o n s t r a t e d t h a t i t i s p o s s i b l e t o

p r o d u c e m e t a l l i c s p e c i e s i n p o l y m e r s by b i n d i n g t h e m e t a l

c a r b o n y l c o m p l e x a n d s u b j e c t i n g c a s t f i l m s o f t h e s e p o l y m e r s t o

m i l d h e a t i n g c o n d i t i o n s . XPS c o n f i r m e d t h e p r e s e n c e o f W03 on

t h e s u r f a c e o f a c o p o l y m e r o f s t y r e n e a n d [W(CO) ( 4 - v p ) ] w h i c h5

h a d b e e n t h e r m a l l y d e c a r b o n y l a t e d . G r o u p 6 m e t a l o x i d e s a r e

e m p l o y e d a s c a t a l y s t s f o r a v a r i e t y o f r e a c t i o n s 6 , WO^ b e i n g a

w e l l known c a t a l y s t f o r o x y g e n e v o l u t i o n a n d t o some e x t e n t f o r

h y d r o g e n e v o l u t i o n 9 8 . U s i n g t h i s t e c h n i q u e i t i s l i k e l y t h a t

e l e m e n t a l m e t a l c a n b e p r o d u c e d by e x c l u d i n g o x y g e n o r b y

r e d u c i n g t h e m e t a l o x i d e s i n s i t u w i t h t o g e n e r a t e h i g h l y

r e a c t i v e m e t a l l i c s p e c i e s . A w i d e v a r i e t y o f m e t a l d i s p e r s i o n s ,

o r e v e n m i x e d m e t a l s y s t e m s , c o u l d b e p r o d u c e d by t h e r m a l

d e c a r b o n y l a t i o n o f m e t a l c a r b o n y l c o m po u n d s a n c h o r e d t o o r g a n i c

s u p p o r t s .

T h e s e e x p e r i m e n t s i n d i c a t e t h e v a r i e t y o f c h e m i s t r y

e x h i b i t e d by s u c h m a t e r i a l s a n d how t h e n a t u r e o f t h e p o l y m e r

c a n i n f l u e n c e t h e d i r e c t i o n o f t h e t h e r m a l r e a c t i o n s . The

c h e m i c a l a n d p h y s i c a l p r o p e r t i e s o f t h e p o l y m e r s u p p o r t a r e

i m p o r t a n t i n d e t e r m i n i n g t h e t h e r m a l r e a c t i o n r o u t e s a v a i l a b l e

t o t h e s e s y s t e m s . By h e a t i n g c a s t f i l m s o f t h e s e p o l y m e r s i t i s

p o s s i b l e t o p r o d u c e h i g h c o n c e n t r a t i o n s o f m e t a l d i s p e r s i o n s

w h i c h may h a v e u s e f u l c a t a l y t i c a c t i v i t y .

140

PRELIMINARY

GROUP 6

CHAPTER 4

PHOTOCHEMICAL STUDIES OF POLYMER-BOUND

METAL CARBONYLS WHEN CAST AS FILMS

141

M e t a l C a r b o n y l s when C a s t a s F i 1 m s

S t u d i e s h a v e d e m o n s t r a t e d t h a t s o l v e n t - c a s t p o l y m e r f i l m

m a t r i c e s may b e u s e d t o s t u d y o r g a n o m e t a l l i e p h o t o c h e m i s t r y a t a

v a r i e t y o f t e m p e r a t u r e s a n d h a v e some a d v a n t a g e s o v e r

h y d r o c a r b o n g l a s s e s 85 a n d p a r a f f i n w a x 102 m a t r i c e s . T h e m a i n

a t t r a c t i o n o f s u c h a p o l y m e r m a t r i x i s t h a t i t e n a b l e s t h e

i s o l a t i o n a n d s t u d y o f u n s t a b l e s p e c i e s a t v e r y l ow t e m p e r a t u r e s

a n d a l l o w s t h e s u b s e q u e n t t h e r m a l r e a c t i o n s o f s u c h s p e c i e s t o

b e m o n i t o r e d o v e r a w i d e t e m p e r a t u r e r a n g e . W h i l e r e p o r t s e x i s t

o f t h e p h o t o l y s i s o f m e t a l h e x a c a r b o n y l s a n d m e t a l c a r b o n y l

c omp ou nd s i n t r o d u c e d i n t o p o l y m e r f i l m s , we r e p o r t t h e

p h o t o l y s i s a t l ow t e m p e r a t u r e s o f s o l v e n t - c a s t o r g a n i c p o l y m e r s

h a v i n g m e t a l c a r b o n y l c o m p l e x e s b o u n d t o t h e m .

The p h o t o c h e m i s t r y o f g r o u p 6 m e t a l c a r b o n y l c o m p l e x e s when

c a s t a s f i l m s a t l ow t e m p e r a t u r e s h a s b e e n i n v e s t i g a t e d .

I n f r a r e d s p e c t r o s c o p i c e v i d e n c e f o r t h e f o r m a t i o n o f a m e t a l

p e n t a c a r b o n y l f r a g m e n t f o r m e d on t h e p h o t o l y s i s o f c o p o l y m e r s o f

s t y r e n e a n d [W(CO)s ( 4 - v p ) ] a t 120 K i s p r e s e n t e d . The i n f l u e n c e

o f t h e p o l y m e r b a c k b o n e on t h e o b s e r v e d p h o t o r e a c t i o n s i s

d i s c u s s e d . P h o t o l y s i s o f p o l y m e r s o f 2 - v i n y l p y r i d i n e r e s u l t s i n

p h o t o d e c a r b o n y l a t i o n .

A b r i e f i n t r o d u c t i o n t o t h e p h o t o c h e m i s t r y o f g r o u p 6 m e t a l

c a r b o n y l s a n d m a t r i x i s o l a t i o n t e c h n i q u e s u s i n g p o l y m e r f i l m s i s

4.1 Preliminary Photochemical Studies of Polymer-Bound Group 6.

142

g i v e n . Some a s p e c t s o f g r o u p 6 m e t a l c a r b o n y l p h o t o c h e m i s t r y

h a v e b e e n p r e v i o u s l y d i s c u s s e d i n s e c t i o n 2 .

4.1.1 The Photochemistry o f Metal Carbonyl Compounds.

I n g e n e r a l , p r i m a r y p h o t o i n d u c e d r e a c t i o n o f m e t a l

c a r b o n y l s i n v o l v e s t h e m o n o d e c a r b o n y l a t i o n p r o c e s s 17' 24' 25 :

M(CO)x — > M(CO)x _ I + CO ( 1 )

The i m p o r t a n c e o f t h e s e p r o c e s s e s l i e i n t h e h i g h q u a n t u m

e f f i c i e n c y a n d a l s o i n t h e n a t u r e o f t h e d e c a r b o n y l a t e d c o m p l e x .

The h i g h q u a n t u m e f f i c i e n c y c a n b e e x p l a i n e d i n s i m p l e t e r m s by

e x a m i n i n g t h e n a t u r e o f t h e b o n d i n g b e t w e e n t h e m e t a l a n d t h e

c a r b o n m o n o x i d e l i g a n d . From a s i m p l i f i e d m o l e c u l a r o r b i t a l

d i a g r a m t h e h i g h e s t o c c u p i e d o r b i t a l s e t a r e p r i n c i p a l l y t h e

m e t a l b a s e d t o r b i t a l s u b - s e t , w h i l e t h e l o w e s t u n o c c u p i e d2 g

o r b i t a l s a r e s t r o n g l y a n t i - b o n d i n g w i t h r e s p e c t t o t h e

e - i n t e r a c t i o n o f t h e c a r b o n y l s . The p h o t o i n d u c e d p r o m o t i o n o f a n*

e l e c t r o n f r o m t h e t o r b i t a l s u b - s e t t o t h e o - o r b i t a l r e m o v e s2g

e l e c t r o n d e n s i t y f r o m t h o s e o r b i t a l s c o n t r i b u t i n g t o t h e

b a c k b o n d i n g i n t e r a c t i o n a n d p o p u l a t e s a n o r b i t a l w h i c h i s

s t r o n g l y a n t i - b o n d i n g w i t h r e s p e c t t o t h e c a r b o n y l

c r - i n t e r a c t i o n . The r e s u l t o f t h i s i s t h e l a b i l i s a t i o n o f t h e

m e t a l c a r b o n y l i n t e r a c t i o n .

143

E x t e n s i v e s t u d i e s o f g r o u p 6 h e x a c a r b o n y l s s u p p o r t v e r y

e f f i c i e n t g e n e r a t i o n o f t h e c o o r d i n a t i v e l y u n s a t u r a t e d

i n t e r m e d i a t e [M(CO)s ] .

M(CO) ---- — ------ t H(CO) + CO ( 2 )6 5

M(CO)s + L ----------------> M(CO)5L ( 3 )

I t i s t h e e x c e p t i o n a l r e a c t i v i t y o f t h e s i x t e e n e l e c t r o n s p e c i e s

w h i c h h a s b e e n t h e s u b j e c t o f many i n v e s t i g a t i o n s , a n d t h e y h a v e

b e e n shown t o i n t e r a c t w i t h many c omp o u n d s c o n s i d e r e d

i n e r t 85' 86 . V i b r a t i o n a l s p e c t r a o f t h e M(CO) s p e c i e s i n low5

t e m p e r a t u r e m a t r i c e s h a v e c o n f i r m e d t h a t i t ' s s t r u c t u r e i s

s q u a r e p y r a m i d a l 85 .

The s y n t h e t i c u t i l i t y o f t h e a b o v e s e q u e n c e h a s h a d

c o n s i d e r a b l e i m p a c t on s y s t e m a t i c s t u d i e s o f t h e M(CO) (L)n 6 - n

c o m p l e x e s . D e r i v a t i v e s o f M(CO) c a n b e p r e p a r e d by i r r a d i a t i o n6

i n t h e p r e s e n c e o f a l m o s t a n y l i g a n d . P h o t o l y s i s o f M(CO)gL

c o u l d r e s u l t i n t h e l o s s o f a n o t h e r CO m o l e c u l e o r l o s s o f L.

L o s s o f CO l e a d s p o t e n t i a l l y t o t wo i s o m e r s o f [M(CO) (L ) ] , a n d4 2

l o s s o f L l e a d s s i m p l y t o l i g a n d e x c h a n g e i n t h e p r e s e n c e o f

a d d e d L.

M(CO) L » M(CO) L + CO ( 4 )5 4

M(CO) L ----------------> M(CO) + L ( 5 )5 5

The r e l a t i v e e f f i c i e n c i e s o f p r o c e s s e s ( 4 ) a n d ( 5 ) w e r e

f o u n d t o b e v e r y s e n s i t i v e t o t h e n a t u r e o f L. The r e l a t i v e

i m p o r t a n c e o f ( 4 ) was f o u n d t o i n c r e a s e w i t h i n c r e a s i n g s t r e n g t h

144

o f t h e M— L b o n d . G e n e r a l l y when L r e s e m b l e s CO i n i t ' s b o n d i n g

p r o p e r t i e s , s e q u e n t i a l s u b s t i t u t i o n o f CO by L i s p o s s i b l e u n t i l

e v e r y CO h a s b e e n r e p l a c e d , e . g . , Mo(CO) c a n b e c o n v e r t e d t o

Mo( P ( OCH ) ) 103. The r e a c t i o n q u a n t u m y i e l d o f ( 4 ) o r ( 5 ) was3 3 6

a l s o f o u n d t o b e s e n s i t i v e t o t h e w a v e l e n g t h o f t h e e x c i t i n g

l i g h t . H i g h e r e n e r g y i r r a d i a t i o n y i e l d s m o r e e f f i c i e n t l o s s o f

CO. The o p p o s i t e w a v e l e n g t h d e p e n d e n c y f o r t h e two p r o c e s s e s ( 4 )

a n d ( 5 ) i s r a t i o n a l i s e d by i n v o k i n g two r e a c t i v e LF e x c i t e d

s t a t e s 17 .

I n t h e p h o t o c h e m i s t r y o f c o mp o u n d s o f M(CO) L ( w h e r e5

L = p y r i d i n e o r a s u b s t i t u t e d p y r i d i n e ) t h e d i r e c t i o n a nd

e f f i c i e n c y o f t h e p h o t o c h e m i c a l p r o c e s s e s d e p e n d s on t h e

e l e c t r o n i c n a t u r e o f a n y s u b s t i t u e n t on t h e p y r i d i n e r i n g

s y s t e m 69 . F o r s u b s t i t u e n t s w h i c h do n o t a f f e c t t h e e n e r g y o f t h e *

n - o r b i t a l on t h e p y r i d i n e l i g a n d , t h e l o w e s t e n e r g y t r a n s i t i o n

i s t h o u g h t t o b e p r i n c i p a l l y a m e t a l c e n t e r e d LF t r a n s i t i o n .

P o p u l a t i o n o f t h e LF s t a t e t e n d s t o r e s u l t i n t h e e f f i c i e n t

p h o t o e x p u l s i o n o f t h e u n i q u e l i g a n d . I n t h e c a s e o f s u b s t i t u e n t s*

w h i c h l o w e r t h e jt - o r b i t a l e n e r g y , t h e l o w e s t e n e r g y t r a n s i t i o n

a s s u m e s some MLCT c h a r a c t e r . I n g e n e r a l p o p u l a t i o n o f MLCT

s t a t e s i n o r g a n o m e t a l l i e c o m p o u n d s r e s u l t s i n p h o t o c h e m i c a l

r e a c t i o n s o f low q u a n t u m e f f i c i e n c y . W(CO) ( p y r i d i n e ) shows5

w a v e l e n g t h d e p e n d e n t p h o t o c h e m i s t r y i n s o l u t i o n . A t 366 nm,

W(CO) i s g e n e r a t e d , s u g g e s t i n g a d i s s o c i a t i v e m e c h a n i s m f o r5

l o s s o f L. At 254 nm, f r e e CO i s d e t e c t a b l e . The r e s u l t s w i t h

t h e p y r i d i n e c o m p l e x e s , h o w e v e r , a r e s o me w h a t a m b i g u o u s , o wi ng

145

t o t h e e s t a b l i s h e d f a c t t h a t s u c h c o m p l e x e s e x h i b i t

M --------> py CT69 i n t h e w a v e l e n g t h r e g i o n w h e r e t h e CO l a b i l i t y

i s o b s e r v e d 69b. L o s s o f CO f r o m M(CO) L (L = 2 , 2 ' - b i p y r i d i n e a n d4

r e l a t e d l i g a n d s ) d o e s o c c u r u p o n p h o t o e x c i t a t i o n i n t o u p p e r

e x c i t e d LF s t a t e s 7 5 . The q u a n t u m e f f i c i e n c i e s a r e s m a l l a n d

w a v e l e n g t h - d e p e n d e n t , a n d t h e MLCT s t a t e i s n o t r e a c t i v e .

I n t e r e s t i n t h e p h o t o a c t i v a t i o n o f t r a n s i t i o n m e t a l

c a r b o n y l s s t e m s i n p a r t f r o m t h e i r p o t e n t i a l u s e a s

p h o t o c a t a l y s t s 17. W r i g h t o n a n d o t h e r s , f o r e x a m p l e , h a v e

d e m o n s t r a t e d t h e c a t a l y t i c a c t i v i t y o f p r o d u c t s d e r i v e d f r o m t h e

p h o t o l y s e s o f M(CO) (M = C r , Mo, o r W) c o m p l e x e s . A l t h o u g h t h e6

l a r g e m a j o r i t y o f wo r k h a s f o c u s e d on p h o t o c a t a l y t i c b e h a v i o u r

i n h o m o g e n e o u s s o l u t i o n , r e c e n t s t u d i e s h a v e b e g u n t o e x p l o r e

t h e p h o t o a c t i v a t i o n o f m e t a l c a r b o n y l s i n p o l y m e r i c• 1 0 2 1 0 6 —1 1 1m a t r i c e s ' " , a n d m o r e r e c e n t l y on s u r f a c e d - c o n f i n e d

m e t a l c a r b o n y l s on p o r o u s g l a s s 112, a s a n a l t e r n a t i v e r o u t e t o

h y b r i d c a t a l y s i s . I n t h i s w o r k , we f o l l o w t h e g e n e r a l t h r u s t f o r

t h e d e v e l o p m e n t o f m o r e e f f i c i e n t h y b r i d - p h a s e c a t a l y s t s . We

w e r e i n t e r e s t e d i n t h e p h o t o c h e m i c a l r e a c t i o n s o f t h e w e l l

c h a r a c t e r i s e d [W(C0) ( p y r i d i n e ) ] a n d c i s - [ W ( C O ) ( b i p y ) ] s y s t e m s5 4

when b o u n d t o p o l y m e r i c s u p p o r t s , a n d i n p a r t i c u l a r t h e

p h o t o g e n e r a t i o n o f c o o r d i n a t i v e l y u n s a t u r a t e d s p e c i e s w h i c h may

b e u s e d a s p o t e n t i a l p h o t o c a t a l y s t s .

146

4.1.2 Matrix I s o l a t i o n i n Polymer M a t r i c e s .

The d e t e c t i o n a n d c h a r a c t e r i s a t i o n o f h i g h l y r e a c t i v e m e t a l

c a r b o n y l f r a g m e n t s h a v e b e e n t h e s u b j e c t o f many i n v e s t i g a t i o n s

i n o r g a n o m e t a l 1 i c c h e m i s t r y . I d e n t i f i c a t i o n o f t h e i n t e r m e d i a t e s

i n a p a r t i c u l a r r e a c t i o n , t h e i r s t r u c t u r e s , a n d how f a s t t h e y

r e a c t i s o f much i n t e r e s t . U n d e r s t a n d i n g t h e s e p r o c e s s e s c a n

l e a d t o a b e t t e r k n o w l e d g e o f t h e m e c h a n i s m s o f o r g a n o m e t a l 1i c

r e a c t i o n s , a n d t o t h e d e v e l o p m e n t o f m o r e e f f i c i e n t

o r g a n o m e t a l 1 i c c a t a l y s t s .

T h e r e h a v e b e e n m a j o r t e c h n i c a l a d v a n c e s i n t h e

p h o t o c h e m i c a l s t u d y o f o r g a n o m e t a l 1 i c r e a c t i o n i n t e r m e d i a t e s .

L a s e r f l a s h p h o t o l y s i s s t u d i e s a r e u s e d w i d e l y f o r t h e d e t e c t i o n

o f i n t e r m e d i a t e s by U V / v i s a b s o r p t i o n on a t i m e s c a l e c o m p a r a b l e

t o t h e f a s t e s t c h e m i c a l p r o c e s s e s i n s o l u t i o n . T h e r e a r e/

l i m i t a t i o n s o f U V / v i s d e t e c t i o n h o w e v e r , d u e t o t h e g e n e r a l

b r o a d n e s s a n d l a c k o f r e s o l v a b l e f i n e s t r u c t u r e i n t h e

e l e c t r o n i c a b s o r p t i o n s o f m o s t o r g a n o m e t a l 1 i c s p e c i e s . T h u s ,

U V / v i s s p e c t r a r a r e l y p r o v i d e much s t r u c t u r a l i n f o r m a t i o n a b o u t

t r a n s i t i o n m e t a l f r a g m e n t s . S u c h i n f o r m a t i o n c a n b e p r o v i d e d by

v i b r a t i o n a l s p e c t r o s c o p y . T i m e - r e s o l v e d i n f r a r e d s p e c t r o s c o p y

a l l o w s t h e IR s p e c t r a o f s h o r t - l i v e d i n t e r m e d i a t e s i n s o l u t i o n

t o b e r e c o r d e d on a m i c r o s e c o n d t i m e s c a l e . I n f r a r e d s p e c t r a a r e

p a r t i c u l a r l y i m p o r t a n t i n c h a r a c t e r i s i n g o r g a n o m e t a l 1i c

i n t e r m e d i a t e s a s t h e y c a n o f t e n p r o v i d e q u i t e d e t a i l e d

s t r u c t u r a l i n f o r m a t i o n . T h e r e h a v e b e e n some m a j o r a d v a n c e s i n

f a s t i n f r a r e d s p e c t r o s c o p y . I t i s now p o s s i b l e t o d e t e c t m e t a l

147

c a r b o n y l i n t e r m e d i a t e s a t room t e m p e r a t u r e i n b o t h s o l u t i o n a n d

g a s p h a s e r e a c t i o n s . The u s e o f l ow t e m p e r a t u r e s o l u t i o n s t o

e x t e n d t h e l i f e t i m e s o f some r e a c t i o n i n t e r m e d i a t e s p r o d u c e d i n

s o l u t i o n , h a s a l l o w e d t h e s e r e a c t i v e s p e c i e s t o b e s t u d i e d . The

i n t e r m e d i a t e c a n b e g e n e r a t e d p h o t o c h e m i c a l 1y a n d t r a p p e d i n a

1o w - t e m p e r a t u r e s o l i d m a t r i x w h i c h p e r m i t s e x a m i n a t i o n o f b o t h

v i b r a t i o n a l a n d e l e c t r o n i c s p e c t r a .

The t e c h n i q u e o f m a t r i x i s o l a t i o n i n v o l v e s t h e i s o l a t i o n o f

a s t a b l e m e t a l c a r b o n y l s p e c i e s i n a l a r g e e x c e s s o f a n i n e r t

s o l i d , t h e m a t r i x . P h o t o l y s i s t h e n g e n e r a t e s t h e u n s t a b l e

f r a g m e n t s . The m o s t common m a t r i x m a t e r i a l s a r e s o l i d g a s e s

( e . g . , n o b l e g a s e s o r CH a t 1 0 - 3 0 K) o r f r o z e n h y d r o c a r b o n s , o r4

m o r e r e c e n t l y p o l y m e r f i l m s . The g r e a t s t r e n g t h o f m a t r i x

i s o l a t i o n i s t h e w i d e r a n g e o f s p e c t r o s c o p i c t e c h n i q u e s w h i c h

c a n b e b r o u g h t t o b e a r on a p a r t i c u l a r i s o l a t e d m e t a l f r a g m e n t .

I n f r a r e d c h a r a c t e r i s a t i o n o f t h e M(CO)g i n t e r m e d i a t e was

B 6f i r s t g a i n e d by S h e l i n e a n d c o w o r k e r s who o b t a i n e d i n f r a r e d

s p e c t r a a f t e r p h o t o l y s i s o f M(CO) a t 77 K i n m e t h y l c y c l o h e x a n e6

g l a s s e s . The s p e c t r a s u p p o r t e d a s s i g n m e n t o f t h e p r i m a r y

p h o t o p r o d u c t a s a C^v M(CO)s . I n a l a t e r wo r k T u r n e r 85 c a r r i e d

o u t p h o t o l y s i s o f g r o u p 6 h e x a c a r b o n y 1s i n 1 o w - t e m p e r a t u r e

m a t r i c e s . P h o t o l y s i s o f M(CO) i n a r g o n a t 20 K y i e l d s M(CO) ,6 5

h a v i n g C^v s y m m e t r y . B o t h i n f r a r e d a n d U V / v i s s p e c t r a l c h a n g e s

w e r e c o n s i s t e n t w i t h t h i s a s s i g n m e n t . The p h o t o g e n e r a t e d M(CO)s

t h e n t h e r m a l l y r e a c t s w i t h p h o t o r e l e a s e d o r a d d e d CO. F o r

148

n u m e r o u s U V / v i s s t u d i e s o f p h o t o p r o d u c e d M(CO) i n many

m a t r i c e s , i t b e ca me c l e a r t h a t t h e v i s i b l e a b s o r p t i o n o f t h e

p e n t a c a r b o n y l i s e x t r e m e l y s e n s i t i v e t o t h e m a t r i x ( SF6

(4 60 n m ) , Ar ( 437 n m ) , Xe ( 417 n m ) , CH4 ( 4 1 3 n m ) ) . As a r e s u l t ,

i t b e c a m e c l e a r t h a t M(C0) i n t e r a c t s w i t h t h e m a t r i x , t h e5

m a t r i x o c c u p y i n g t h e s i x t h c o o r d i n a t i o n s i t e .

The p h o t o c h e m i s t r y o f g r o u p 6 m e t a l c a r b o n y l s i n p o l y m e r

f i l m s was f i r s t s t u d i e d by M a s s e y a n d O r g e l 104. Th e y f o u n d t h a t

i r r a d i a t i n g a m e t h y l m e t h a c r y l a t e p o l y m e r c o n t a i n i n g a s m a l l

a m ou n t o f m e t a l h e x a c a r b o n y l a t r oom t e m p e r a t u r e p r o d u c e d a d e e p

y e l l o w c o l o u r . Th e y p r o p o s e d t h a t t h e M(CO) f r a g m e n t h a d b e e n5

f o r m e d . The f r a g m e n t was f o u n d t o b e s t a b l e a t l i q u i d n i t r o g e n

t e m p e r a t u r e s . On l e a v i n g t h e p o l y m e r i n t h e d a r k t h e p a r e n t

h e x a c a r b o n y l r e f o r m e d . I t was a l m o s t t e n y e a r s l a t e r when

M c I n t y r e r e p o r t e d t h a t t h e t h e r m a l b a c k r e a c t i o n u p o n p h o t o l y s i s

o f Cr (CO) i n a p o l y s t y r e n e f i l m o c c u r r e d a t a much s l o w e r r a t e 6

1.0 5t h a n i n c y c l o h e x a n e s o l u t i o n . T h i s h e a t t r i b u t e d t o t h e

g r e a t l y d e c r e a s e d m o b i l i t y o f CO i n c y c l o h e x a n e r e l a t i v e t o

p o l y s t y r e n e . S i n c e M c I n t y r e ' s e x p e r i m e n t , t h e u s e o f p o l y m e r

m a t r i c e s f o r s t u d y i n g m e t a l c a r b o n y l p h o t o c h e m i s t r y h a d n o t b e e n

r e p o r t e d i n e r n e s t u n t i l R e s t a n d c o w o r k e r s p r o d u c e d a s e r i e s o f

p u b l i c a t i o n s on t h e g e n e r a t i o n o f m e t a l c a r b o n y l i n t e r m e d i a t e s

i n p o l y m e r f i l m s o v e r a w i d e r a n g e o f t e m p e r a t u r e s .

i n oI n o n e s u c h r e p o r t , H o o k e r a n d R e s t s t u d i e d t h e

p h o t o c h e m i s t r y o f g r o u p 6 h e x a c a r b o n y l s i n PVC f i l m s . Room

149

THF, a f f o r d e d b a n d s a t 2 0 7 4 , 1 9 2 9 a n d 1887 cm-1 (M = W) w i t h a

r e d u c t i o n o f t h e p a r e n t b a n d s . The f i l m , w h i c h h a d t u r n e d

y e l l o w , a l s o e x h i b i t e d a new a b s o r p t i o n a t 420 nm. A s l o w

r e v e r s a l o f t h e r e a c t i o n o c c u r r e d on l e a v i n g t h e p o l y m e r i n t h e

d a r k f o r s e v e r a l d a y s . I r r a d i a t i o n o f W(CO) u n d e r t h e same6

c o n d i t i o n s i n a PVC f i l m c a s t f r o m 1 , 2 - d i c h l o r o e t h a n e s o l u t i o n

a l s o p r o d u c e d t h r e e new IR b a n d s b u t a t h i g h e r w a v e n u m b e r s

( 2 0 8 0 , 1932 a n d 1887 cm- 1 ) . I n c o n t r a s t , t h e r m a l r e v e r s a l o f t h e

r e a c t i o n o c c u r r e d o n l y a f t e r a f ew m i n u t e s . R e s t a s s i g n e d t h e

c o m p l e x f o r m e d i n p o l y m e r f i l m s i n w h i c h THF i s p r e s e n t t o

W( CO) ( THF) . UV i r r a d i a t i o n o f M(CO) (M = Cr o r Mo) i n t h e s e5 6

f i l m s r e s u l t e d i n t h e f o r m a t i o n o f t h e s p e c i e s M(CO) ( T HF) . I n5

p h o t o l y s i s o f W(CO) i n f i l m s a t 12 K new IR b a n d s a p p e a r e d a t6

2 0 8 4 , 1 9 4 6 a n d 1918 ( s h ) cm- 1 , t o g e t h e r w i t h a b a n d f o r f r e e CO

a t 2135 cm“ 1 w i t h a n a c c o m p a n y i n g d e c r e a s e i n t h e p a r e n t b a n d s .

The p h o t o r e a c t i o n r e v e r s e d a t 12 K on i r r a d i a t i o n w i t h v i s i b l e

l i g h t . On s l o w w a r m i n g t h e p r o d u c t b a n d s d e c r e a s e d w i t h

r e g e n e r a t i o n o f t h e h e x a c a r b o n y l b a n d s . T h e p r o d u c t b a n d s w e r e

a s s i g n e d t o t h e W(CO)g f r a g m e n t a n d was t h o u g h t t o b e s t a b i l i s e d

b y i n t e r a c t i o n s w i t h t h e p o l y m e r m a t r i x .

I n a n o t h e r r e p o r t , R e s t e t a 1. i n v e s t i g a t e d t h e

p h o t o c h e m i c a l r e a c t i o n s o f CpMo(CO) (CH ) (Cp = r\5-C H ) i n PVC3 3 5 5

f i l m s i n t h e r a n g e 1 0 - 2 9 3 K106. On i r r a d i a t i o n a t 12 K, t h e y

o b s e r v e d c h a n g e s i n t h e c a r b o n y l s t r e t c h i n g f r e q u e n c y r e g i o n o f

t h e IR c o n s i s t e n t w i t h t h e f o r m a t i o n o f CpMo(CO)2 (CH3 ) a n d

temperature UV irradiation (X < 350 nm) of a film cast from

150

CpMo(CO)3 . F u r t h e r i r r a d i a t i o n p r o d u c e d b a n d s t h e y a s s i g n e d t o

CpMo(CO)3C l , f o r m e d f r o m r e a c t i o n o f p h o t o c h e m i c a l l y p r o d u c e d

CpMo( C0) 3 r a d i c a l s w i t h t h e PVC m a t r i x . I n s i m i l a r s t u d i e s i n

PVC a t 12 K, p h o t o l y s i s o f CpM(CO) (C H ) r e s u l t s i n l o s s o f3 2 5

CO107. The p h o t o p r o d u c t r e a r r a n g e s t h e r m a l l y t o f o r m

t r a n s - C p M ( C O ) 2 (C2H4)H.

De P a o l i a n d c o w o r k e r s 108 r e p o r t e d s t u d i e s o f t h e

p h o t o c h e m i c a l r e a c t i o n s o f p e n t a c a r b o n y l i r o n w i t h o l e f i n s i n a

PTFE room t e m p e r a t u r e m a t r i x . The r e a c t i o n s o f t h e d i e n e s

b u t a d i e n e a n d i s o p r e n e i n t h e m a t r i x p r o d u c e d n o t o n l y

d i e n e t r i c a r b o n y l i r o n b u t a l s o b i s ( d i e n e ) m o n o c a r b o n y l i r o n

c o m p o u n d s . W i t h e t h y l e n e a n d a c e t y l e n e t h e y o b s e r v e d t h e

f o r m a t i o n o f e t h y l e n e t e t r a c a r b o n y l i r o n a n d

a c e t y l e n e t e t r a c a r b o n y l i r o n . H o o k e r a n d R e s t i n v e s t i g a t e d t h e

p h o t o l y s i s o f a c e t y l d i c a r b o n y l (T7 S- c y c l o p e n t a d i e n y l ) i r o n

c o m p l e x e s i n PVC m a t r i c e s a t 1 2 - 2 0 0 K. The p h o t o i n d u c e d

d e c a r b o n y l a t i o n o f C p F e ( C O ) z (COCH3 ) was f o u n d t o b e t h e r m a l l y

r e v e r s i b l e . The d e c a r b o n y l a t e d s p e c i e s c o u l d n o t b e g e n e r a t e d i n

c o n v e n t i o n a l f r o z e n m a t r i c e s e v e n u n d e r v i g o r o u s i r r a d i a t i o n

c o n d i t i o n s . They s u g g e s t e d t h a t t h i s f a i l u r e was d u e t o a r a p i d

b a c k r e a c t i o n o f t h e p h o t o g e n e r a t e d f r a g m e n t s i n t h e c l o s e l y

c o n f i n e d g a s m a t r i x e n v i r o n m e n t . I n c o n t r a s t , t h e p o l y m e r f i l m

m a t r i c e s a r e t h o u g h t t o p r o v i d e a m o r e c a v e r n o u s m e d i u m 110 i n

w h i c h t h e " c a g e e f f e c t " i s a l e s s s e r i o u s p r o b l e m .

151

A n u m b e r o f s t u d i e s h a v e d e m o n s t r a t e d t h e p o t e n t i a l o f

p o l y m e r f i l m s f o r i n v e s t i g a t i n g t h e p h o t o r e a c t i o n s o f

o r g a n o m e t a l l i e c o m p o u n d s . R e a c t i v e i n t e r m e d i a t e s c a n b e t r a p p e d

a n d s t u d i e d a t c r y o g e n i c t e m p e r a t u r e s i n a s i m i l a r a n d

c o m p l e m e n t a r y f a s h i o n t o s t u d i e s i n i n h y d r o c a r b o n g l a s s e s a n d

f r o z e n g a s m a t r i c e s . U s i n g p o l y m e r f i l m s , s t a b i l i t i e s o f

p h o t o p r o d u c e d i n t e r m e d i a t e s c a n b e s t u d i e d o v e r a f a r g r e a t e r

t e m p e r a t u r e r a n g e , a n d De P a o l i 108 s u g g e s t e d t h a t a p o l y m e r f i l m

a t 293 K was a p o s s i b l e r e p l a c e m e n t f o r e l a b o r a t e g a s m a t r i x

i s o l a t i o n s t u d i e s r e q u i r i n g e x p e n s i v e c r y o g e n i c e q u i p m e n t .

I n d e e d , u s i n g p o l y m e r f i l m m a t r i c e s i t i s p o s s i b l e t o t r a p a t

1o w - t e m p e r a t u r e s r e a c t i v e s p e c i e s w h i c h c a n n o t b e f o r m e d by

s i m i l a r in situ p h o t o l y s i s o f m o l e c u l e s i n c o n v e n t i o n a l f r o z e n

g a s m a t r i c e s 109. I n t h e c a s e o f 1 o w - t e m p e r a t u r e m a t r i c e s t h e

s o r t s o f r e a c t i o n s t h a t may o c c u r p h o t o c h e m i c a l 1 y a r e v e r y

l i m i t e d by t h e r e s t r i c t i o n s o f t h e s o c a l l e d " c a g e e f f e c t "

I t i s g e n e r a l l y d i f f i c u l t t o p r o d u c e a s p e c i e s by a n i n situ

p h o t o l y s i s i n 1o w - t e m p e r a t u r e m a t r i c e s b y p h o t o e j e c t i o n o f a

l i g a n d b e c a u s e t h e m o l e c u l e i s t o o l a r g e t o s q u e e z e r e a d i l y

t h r o u g h l a t t i c e i n t e r s t i c e s a n d away f r o m t h e n e w l y f o r m e d

u n s t a b l e s p e c i e s . T h u s , i n t h e 1o w - t e m p e r a t u r e m a t r i c e s , t h e two

f r a g m e n t s h e l d t o g e t h e r i n t h e m a t r i x c a g e r e c o m b i n e t o r e f o r m

t h e p a r e n t m o l e c u l e . I n room t e m p e r a t u r e p o l y m e r m a t r i c e s t h e

m o l e c u l e s h e l d i n t h e a m o r p h o u s s i t e s a p p a r e n t l y h a v e a much

h i g h e r m o b i l i t y , i n s u c h a way t h a t a c a r b o n m o n o x i d e l i g a n d c a n

d i f f u s e away a n d t h e o t h e r l i g a n d a p p r o a c h e s t h e c o o r d i n a t i v e l y

u n s a t u r a t e d s p e c i e s f o r m e d .

152

p h o t o p r o d u c t s c o u l d b e " f r o z e n " i n t h e p o l y m e r m a t r i x i n a"102 ,m a n n e r s i m i l a r t o t h a t d e v e l o p e d by H o o k e r a n d R e s t . I n t h i s

i n s t a n c e , h o w e v e r , t h e p a r e n t m e t a l c a r b o n y l c o m p l e x e s a r e b o u n d

t o t h e p o l y m e r m a t r i x . T h i s m e t h o d p r o v i d e s t h e a d v a n t a g e o f

b e t t e r m e t a l c a r b o n y l d i s t r i b u t i o n i n t h e p o l y m e r m a t r i x , a s

s o a k i n g p o l y m e r s v e r y o f t e n r e s u l t s i n h i g h l o c a l c o n c e n t r a t i o n s

o f s p e c i e s a nd t h e p r e s e n c e o f a g g r e g a t e s i n t h e s e f i l m s .

H o w e v e r , t h e n u m b e r a n d b r o a d n e s s o f t h e b a n d s make t h e

a t t a i n m e n t o f s p e c t r a l i n f o r m a t i o n m o r e d i f f i c u l t t h a n t h o s e

s t u d i e s o f m e t a l h e x a c a r b o n y 1s wh ose s p e c t r a a r e l e s s d e t a i l e d .

I n t h i s s t u d y , i t was o f i n t e r e s t n o t o n l y t o i n v e s t i g a t e t h e

p h o t o c h e m i s t r y o f m e t a l c a r b o n y l s b o u n d t o p o l y m e r s u p p o r t s , b u t

i m p o r t a n t l y t o e x a m i n e t h e e f f e c t o f t h e p o l y m e r b a c k b o n e on t h e

p h o t o c h e m i c a l r e a c t i o n r o u t e s .

4 . 2 L o w - T e m p e r a t u r e P h o t o l y s i s o f P o l y m e r - B o u n d G ro u p 6. M e t a l

C a r b o n y l s .

I n t h e s e e x p e r i m e n t s t h e p o l y m e r f i l m s w e r e c a s t a s f i l m s

on a s a p p h i r e s u p p o r t . The f i l m s w e r e pumped u n d e r v a c u u m t o

r e m o v e a n y t r a c e s o f s o l v e n t , a n d f i t t e d i n a v a r i a b l e

t e m p e r a t u r e i n f r a r e d c e l l a n d c o o l e d t o 120 K. The s a m p l e s w e r e

t h e n e x p o s e d t o b r o a d - b a n d r a d i a t i o n f r o m a l ow p r e s s u r e m e r c u r y

l a m p , f i l t e r e d t h r o u g h t h e s o d i u m c h l o r i d e wi n d o ws o f t h e

v a r i a b l e t e m p e r a t u r e c e l l . Any s p e c t r a l c h a n g e s w e r e m o n i t o r e d

i n t h e c a r b o n y l s t r e t c h i n g f r e q u e n c y r e g i o n o f t h e i n f r a r e d _ *

( 2 2 0 0 - 1 7 0 0 cm" ) . A l l p h o t o l y s i s e x p e r i m e n t s w e r e c a r r i e d o u t in

vacuo.

In this research it was hoped that any reactive

153

I r r a d i a t i o n o f a c o p o l y m e r o f s t y r e n e a n d [W(CO) ( 4 - v p ) ] a t5

120 K r e s u l t e d i n t h e a p p e a r a n c e o f a new IR b a n d a t 2077 cm-1

( s h o u l d e r i n g t h e h i g h f r e q u e n c y c h a r a c t e r i s t i c p e n t a c a r b o n y 1

b a n d ) t o g e t h e r w i t h a b a n d f o r f r e e CO a t 2139 cm- 1 , a t t h e

e x p e n s e o f t h e p a r e n t b a n d s ( s e e F i g u r e 4 . 2 . 1 ) . The b r o a d n e s s o f

t h e r e m a i n i n g c a r b o n y l b a n d s p r e c l u d e d a n y s i g n i f i c a n t s p e c t r a l

c h a n g e s b e i n g o b s e r v e d b e l o w 2000 cm- 1 . T h e r m a l r e v e r s a l o f t h e

r e a c t i o n o c c u r r e d on w a r mi n g t h e f i l m t o 200 K. The p r i m a r y

p h o t o p r o d u c t was a s s i g n e d t o t h a t o f a p e n t a c a r b o n y l s p e c i e s

w h i c h i s no l o n g e r a t t a c h e d t o t h e p o l y m e r b a c k b o n e v i a t h e

p e n d a n t n i t r o g e n a t o m o f a p y r i d i n e m o i e t y . T h i s i s n o t

s u r p r i s i n g s i n c e t h e p r i m a r y p h o t o r e a c t i o n o f [W( CO) ( p y r i d i n e ) ]

i s l o s s o f t h e p y r i d i n e l i g a n d 17. R e s t r e p o r t e d t h a t t h e UV

p h o t o l y s i s o f [W(CO) ( p y r i d i n e ) ] i s o l a t e d a t h i g h d i l u t i o n i n5

m e t h a n e m a t r i c e s a t 10 K, p r o d u c e s new IR a b s o r p t i o n s a s s o c i a t e d

w i t h W(CO) a n d f r e e l i g a n d 111. H o w e v e r , on t h e b a s i s o f m a t r i x5

85 102 79 81i s o l a t i o n ' a n d f l a s h p h o t o l y s i s e x p e r i m e n t s , i t i s

t h o u g h t u n l i k e l y t h a t t h i s p e n t a c a r b o n y l s p e c i e s i s

c o o r d i n a t i v e l y u n s a t u r a t e d , b u t r a t h e r i n t e r a c t s w i t h s i t e s o f

e l e c t r o n d e n s i t y on t h e p o l y m e r , p o s s i b l y t h e a r o m a t i c m o i e t i e s .

On w a r mi n g t h i s s a m p l e t o room t e m p e r a t u r e , t h e s p e c t r a l c h a n g e s

w e r e f o u n d t o r e v e r s e , i n d i c a t i n g t h a t on h e a t i n g , t h e

p h o t o p r o d u c e d p e n t a c a r b o n y l a g a i n r e a c t s w i t h t h e n i t r o g e n s i t e s

on t h e p o l y m e r b a c k b o n e . T h i s r e v e r s a l s u g g e s t s t h a t

p h o t o e j e c t e d CO m o l e c u l e s a n d W(CO) f r a g m e n t s do n o t d i f f u s e5

away f r o m t h e p h o t o l y s i s s i t e s a t v e r y low t e m p e r a t u r e s . P o l y m e r

4.2.1 A Copolymer of S t y r e n e and W(CO)5 ( v i n y l p y r i d i n e ) .

154

m a t r i c e s a r e t h o u g h t t o p r o v i d e a m o r e c a v e r n o u s med i um s o t h a t

p r o b l e m s o f r e c o m b i n a t i o n on p h o t o l y s i s f o u n d i n o t h e r

1o w - t e m p e r a t u r e m a t r i c e s do n o t o c c u r . The p h o t o e j e c t e d

W(C0) c a n "move" r e a d i l y t h r o u g h t h e s p a c e s i n t h e p o l y m e r5

m a t r i x away f r o m t h e p e n d a n t s i t e s on t h e p o l y m e r .

P h o t o l y s i s o f a f i l m o f a c o p o l y m e r o f s t y r e n e a n d

[W(CO) ( 2 - v p ) ] a t 120 K, r e s u l t e d i n t h e d e c r e a s e o f t h e5

s t r e t c h i n g f r e q u e n c i e s o f t h e c h a r a c t e r i s t i c o f t h e

p e n t a c a r b o n y l s p e c i e s t o g i v e a p h o t o d e c a r b o n y l a t e d p o l y m e r ( s e e

F i g u r e 4 . 2 . 2 ) . E v i d e n c e f o r t h e f o r m a t i o n o f f r e e c a r b o n

m o n o x i d e was f o u n d f r o m t h e p r o d u c t i o n o f a b a n d a t 2 1 29 cm- 1 .

T h i s r e a c t i o n was n o t r e v e r s i b l e on w a r m i n g t o room t e m p e r a t u r e .

The r e a s o n f o r t h e d i f f e r e n c e s i n t h e p h o t o c h e m i c a l b e h a v i o u r o f

p o l y m e r s o f 2 - a n d 4 - v i n y l p y r i d i n e i s u n c e r t a i n . Th e y b o t h

i n i t i a l l y c o n t a i n m e t a l p e n t a c a r b o n y l f r a g m e n t s b o u n d t o t h e

p o l y m e r t h r o u g h a m e t a l t o n i t r o g e n b o n d i n i d e n t i c a l

e n v i r o n m e n t s .

155

F i g . 4 . 2 . 1 C h a n g e s o b s e r v e d i n t h e c a r b o n y l s t r e t c h i n g r e g i o n o f t h e i n f r a r e d on UV p h o t o l y s i s o f a f i l m o f a c o p o l y m e r o f

s t y r e n e a n d [W(CO) ( 4 - v p ) ] a t 120 K.5

220*3 2 1 0 0 2000 i 900 1800 1700

wavenumbers (cm- 1 )

UV photolysis at 120 K results in the p r o d u c t i o n a t h e r m a l l y

unstable m e t a l pentacarbonyl f r a g m e n t ( 2 0 7 7 c m ^ s h ) with some

m e t a l centers s u f f e r i n g photodecarbonylation (free CO at

2139 cm ) . War ming the s a m p l e gradually to room t e m p e r a t u r e r e s u l t s i n t h e disappearance of the new bands with regeneration

of the p a r e n t pentacarbonyl.

156

F i g . 4 . 2 . 2 UV p h o t o l y s i s o f a c a s t f i l m o f a p o l y m e r o f s t y r e n e a n d [ W(C0)5 ( 2 - v p ) ] a t 120 K m o n i t o r e d by o b s e r v i n g t h e c h a n g e s

i n t h e i n f r a r e d s p e c t r u m ( 2 2 0 0 - 1 7 7 0 cm u) .

2200 2100 2000 1900 1800 1700

wavenumbers ( cm- 1)

UV photolysis results in complete photodecarbonylation of the

metal centers a f t e r o n e h o u r . The r e a c t i o n i s not r e v e r s i b l e on w a r m i n g t o room temperature.

157

I r r a d i a t i n g a c o p o l y m e r o f e t h y l a c r y l a t e a nd

[W(CO) ( 4 - v p ) ] a t l ow t e m p e r a t u r e s l e a d t o t h e a p p e a r a n c e o f5

g r o w - i n b a n d s a t 2 0 1 0 , 1866 ( s h ) , a n d 1831 cm 1 ( F i g u r e 4 . 2 . 3 ) .

Some f r e e CO was d e t e c t e d a t 2131 cm- 1 . The b r o a d n e s s o f t h e

p a r e n t p e n t a c a r b o n y l b a n d s p r e v e n t e d t h e a t t a i n m e n t o f f u r t h e r

s p e c t r a l i n f o r m a t i o n . On w a r m i n g t h e s a m p l e t o room t e m p e r a t u r e ,

t h e b a n d s d e c r e a s e d i n i n t e n s i t y t o g e t h e r w i t h a n a c c o m p a n y i n g

i n c r e a s e i n t h e p a r e n t p e n t a c a r b o n y l f r e q u e n c i e s . S i m i l a r

s p e c t r a l c h a n g e s w e r e r e c o r d e d on p h o t o l y s i s o f a c o p o l y m e r o f

m e t h y l a c r y l a t e a n d [W(CO) ( 4 - v p ) ] .5

I t i s p r o p o s e d t h a t t h e p r i m a r y p h o t o r e a c t i o n i s l o s s o f a

CO l i g a n d t o f o r m t h e t e t r a c a r b o n y l s p e c i e s , w h i c h t h e n

c o o r d i n a t e s t o a n o x y g e n s i t e on t h e a c r y l a t e b a c k b o n e . B o n d i n g

t h r o u g h o x y g e n i s l e s s e f f e c t i v e t h a t t h r o u g h n i t r o g e n , a n d

c o o r d i n a t i o n v i a t wo n i t r o g e n d o n o r s w o u l d b e e x p e c t e d t o

p r o d u c e a m o r e s t a b l e t e t r a c a r b o n y l s p e c i e s . To i n v e s t i g a t e t h i s

f u r t h e r , a p o l y m e r o f [W(CO) ( 4 - v p ) ] a n d 4 - v i n y l p y r i d i n e was5

p h o t o l y s e d a t l o w - t e m p e r a t u r e . F i g u r e 4 . 2 . 4 s ho ws t h e c h a n g e s

o b s e r v e d i n t h e c a r b o n y l s t r e t c h i n g r e g i o n on p h o t o l y s i s o f a

f i l m o f t h i s p o l y m e r . B a n d s a t 2 0 0 3 , 1 8 8 1 ( s h ) a n d 1 8 2 5 cm-1 a n d

a b a n d d u e t o f r e e CO ( 2 1 3 2 cm- 1 ) a r e f o r m e d w i t h a r e d u c t i o n i n

t h e i n t e n s i t y o f t h e p a r e n t b a n d s . On h e a t i n g t o 20°C, t h e b a n d

d u e t o CO g r a d u a l l y d e c r e a s e d i n i n t e n s i t y a s t h e CO d i f f u s e d

o u t o f t h e p o l y m e r m a t r i x . H o w e v e r , no c h a n g e i n i n t e n s i t y o f

t h e p h o t o p r o d u c e d b a n d s was o b s e r v e d . T h e s e b a n d s a r e c l o s e t o

4 . 2 . 2 P h o t o l y s i s o f M et a l Ca rbo ny l C o n t a i n i n g A c r y l a t e P o l y m e r s .

158

those reported for cis-[W(CO) (py) ]7°, and so it is proposed4 2

that the disubstituted tetracarbonyl species is formed following

photoejection of a CO ligand. The tetracarbonyl formed through

coordination through two pyridine residues is thermally stable

suggesting that in the case of the acrylate polymers, the

photoproduced tetracarbonyl is stabilised by interactions with

the oxygen sites on the polymer backbone.

Strohmeier24b, upon irradiation of [W(CO) (pyridine)] in5

the presence of excess pyridine, reported the formation of

[W(CO) (py) ] in solution. He postulated that [M(CO) (py)]4 2 5

photodissociates into [M(CO) (py)] (following photoexpulsion of4

an equatorial CO ligand) and into [M(CO) ] (as a result of5

photocleavage of the metal to pyridine bond) simultaneously with

an overall quantum yield of unity. While the first intermediate

[M(CO) (py)] yields the product [M(CO) (py) ], the second4 4 2

intermediate [M(CO) ] should react with additional pyridine to5

give back the starting complex and so does not contribute to the

net reaction. In the case of the 4-vinylpyridine copolymer, the

local concentration of uncoordinated pyridine in the vicinity of

any photoproduced [M(CO) ] would be high so that the rate ofsrecombination would be expected to be high also. Further

evidence for this was found on irradiating a terpolymer of

styrene and [M(CO) (vp)] containing 4-vinylpyridine (10/1 mole5

ratio of styrene/4-vinylpyridine). Irradiation resulted in the

appearance of a new band at 2077 cm-1 which disappeared on

raising the temperature. Bands assignable to cis-[W(CO) (py) ]704 2

159

and free CO were also found. Thus, in the absence of a large

excess of pyridine sites on the polymer backbone, matrix

isolated [W(CO) ] is observed because the likelihood of5

encountering a recombination site is decreased. It has been

previously reported that the quantum yield for photodissociation

of the [W(CO) (4-vp)] complex in styrene-5

4-vinylpyridine-[W(CO) (4-vp)] terpolymers in solution is5

dependent on the nature of the polymer backbone, and in

particular on the proportion of uncoordinated vinylpyridinen qgroups on the chain . Lower quantum yields were attributed to

recombination of the initially formed [W(CO) ] with other5

uncoordinated pyridine groups of the polymer. The same can be

stated for polymer films at 1ow-temperatures.

In sharp contrast to those polymers of ethyl or methyl

acrylate, irradiation of a copolymer of methylmethacrylate and

[W(CO)s(4-vp)] at low-temperature yielded a totally

photodecarbonylated polymer. The difference in photoreactivity

is not clear as both contain metal pentacarbonyls bound via a

metal-nitrogen bond in polymer backbones of similar chemical

composition. It is thought unlikely that the difference because

of a difference in chain mobility of the two polymers. Motion of

polymer chains probably ceases at low temperatures but the

polymer matrix does not become too rigid to prevent the

photoejection of the bulky ligand [W(CO) ].5

160

Copolymers of styrene, methylmethacrylate, and ethyl

acrylate containing bound [W(CO) (4-vinyl-4'-methyl-2,2'-bipy)]4

did not exhibit any photoreactivity. Prolonged UV photolysis at

low temperatures afforded no change in the tetracarbonyl bands

in the infrared. Unlike complexes of the type [W(CO) (pyridine)]5

where the lowest excited state is a ligand field transition, the

lowest energy transition of [W(CO) (bipy)] complexes assumes4

some metal-to-ligand charge transfer character (MLCT), and as

previously stated population of MLCT states in organometallie

compounds results in photochemical reactions of low quantum

efficiency.

4 . 2 . 3 Photolysis o f P o l y m e r s C o n t a i n i n g M e ta l T e t r a c a r b o n y l .

161

Fig. 4.2.3 Infrared spectral changes observed on UV photolysis of a cast film of a copolymer of ethyl acrylate and [W(CO) (4-vp)] at 120 K.

5

21@0 2O00 1900 1800 1700

wavenumbers (cm- 1)

UV photolysis at 120 K results in the formation of a thermally unstable tetracarbonyl species thought to be formed through coordination through pyridine and oxygen on the polymer backbone.

162

F i g . 4 . 2 . 4 C h a n g e s o b s e r v e d i n t h e i n f r a r e d ( 2 2 0 0 - 1 7 0 0 c m ' 1) on p h o t o l y s i s o f a c o p o l y m e r o f 4 - v i n y l p y r i d i n e a n d [W(CO)s ( 4 - v p ) ]

a t 120 K.

2000 1500 1800 1700

wavenumbers (cm- 1 )

On photolysis, a t h e r m a l ly stable c i s - f W ( C O ) (py) ]4 2

tetracarbonyl species is p r o d u c e d .

163

4 . 3 C o n c l u s i o n s

The p h o t o l y s i s o f s t y r e n e a n d [W(CO) ( 4 - v p ) ] p o l y m e r s5

g e n e r a t e s a n a c t i v e c o o r d i n a t e l y u n s a t u r a t e d m e t a l c a r b o n y l

s p e c i e s a t l ow t e m p e r a t u r e s , w h i c h was f o u n d t o b e t h e r m a l l y

u n s t a b l e . T h i s r e s u l t i n d i c a t e s t h e f o r m a t i o n o f a s p e c i e s w h i c h

c o u l d e x h i b i t c a t a l y t i c a c t i v i t y . I n t h e c a s e o f p o l y m e r s o f

2 - v i n y l p y r i d i n e e v i d e n c e f o r p h o t o d e c a r b o n y l a t i o n was o b t a i n e d .

T h i s c o u l d r e p r e s e n t a s i m p l e a n d e f f i c i e n t m e a n s o f

i n c o r p o r a t i n g m e t a l d i s p e r s i o n s i n p o l y m e r i c f i l m s by p h o t o l y t i c5 3 BB 9 0m e a n s . On t h e b a s i s o f r e p o r t e d e x p e r i m e n t s , i t i s

l i k e l y t h a t m e t a l o x i d e s o r e l e m e n t a l m e t a l c o u l d b e g e n e r a t e d

i n t h e s e f i l m s by p h o t o l y s i s o f t h e b o u n d m e t a l p e n t a c a r b o n y l .

T h i s m e t h o d c o u l d o v e r c o m e p r o b l e m s a s s o c i a t e d w i t h c o n v e n t i o n a l

m e t h o d s o f p r e p a r i n g c o l l o i d a l d i s p e r s i o n s s u c h a s u n i f o r m i t y o f

d i s p e r s i o n a n d s i z e o f t h e a g g r e g a t e s . By p r e p a r i n g p o l y m e r s

c o n t a i n i n g m e t a l c a r b o n y l s t h e d i s t r i b u t i o n / l o a d i n g o f t h e m e t a l

c o m p l e x c a n b e c o n t r o l l e d s o t h a t p h o t o l y t i c d e c o m p o s i t i o n may

p r o d u c e d i s p e r s i o n s o f l ow d i a m e t e r a n d o f h i g h u n i f o r m i t y . I n

t h i s way m e t a l d i s p e r s i o n s c o u l d b e p r e p a r e d , w i t h o u t t h e n e e d

f o r e l a b o r a t e e q u i p m e n t o r p r o c e d u r e s , a t room t e m p e r a t u r e .

P h o t o l y s i s o f a c r y l a t e p o l y m e r s r e s u l t s i n t h e

p h o t o g e n e r a t i o n o f a t h e r m a l l y u n s t a b l e t e t r a c a r b o n y 1 s p e c i e s

w h i c h i s t h o u g h t t o b e s t a b i l i s e d b y o x y g e n i n t e r a c t i o n s a t

l o w - t e m p e r a t u r e s . T h o s e p o l y m e r s o f m e t h y l m e t h a c r y 1 a t e s u f f e r

c o m p l e t e p h o t o d e c a r b o n y l a t i o n . E x p e r i m e n t s i n c o r p o r a t i n g f r e e

u n c o o r d i n a t e d p y r i d i n e i n t o t h e p o l y m e r b a c k b o n e i n d i c a t e t h a t

164

t h e p h o t o c h e m i c a l r e a c t i o n r o u t e s o f f i l m s o f p o l y m e r s

c o n t a i n i n g [W(C0)s ( 4 - v p ) ] , d e p e n d on t h e p r o p o r t i o n o f f r e e

p y r i d i n e on t h e p o l y m e r c h a i n . I n t h e p r e s e n c e o f e x c e s s

p y r i d i n e b i n d i n g s i t e s , t h e c i s - t e t r a c a r b o n y l s p e c i e s i s f o r m e d .

Low c o n c e n t r a t i o n s f a v o u r t h e f o r m a t i o n o f [W(CO) ] . The5

p h o t o e x p u l s i o n o f a CO l i g a n d f r o m [W(CO) ( 4 - v p ) ] , p r o d u c e s a5

p o l y m e r - b o u n d c o o r d i n a t i v e l y u n s a t u r a t e d s i t e . S u i t a b l e

s u b s t r a t e m o l e c u l e s c o u l d b e i n c o r p o r a t e d i n t o t h e p o l y m e r

m a t r i x i n a m a n n e r s i m i l a r t o t h a t d e s c r i b e d b y De P a o l i a n d

c o w o r k e r s who s t u d i e d t h e r e a c t i o n s o f p e n t a c a r b o n y l i r o n w i t h108o l e f i n s i n p o l y m e r m a t r i c e s a t room t e m p e r a t u r e . On

p h o t o e x p u l s i o n o f a CO l i g a n d , a s u b s t r a t e m o l e c u l e c o u l d b e

b o u n d a n d s o i n i t i a t e c a t a l y s i s .

P h o t o l y s i s o f t h i n f i l m s o f t h e s e p o l y m e r - b o u n d m e t a l

c a r b o n y l s a t 1o w - t e m p e r a t u r e s r e s u l t s i n t h e p r o d u c t i o n o f

s p e c i e s w h i c h c o u l d h a v e c a t a l y t i c p o t e n t i a l . E v i d e n c e f o r f u l l

p h o t o d e c a r b o n y l a t e d m e t a l c e n t e r s was a l s o f o u n d s u g g e s t i n g t h a t

t h i s t e c h n i q u e c o u l d b e u t i l i s e d t o p r o d u c e m e t a l d e p o s i t s i n

p o l y m e r m a t r i c e s . T h e s e e x p e r i m e n t s h a v e shown t h a t t h e p o l y m e r

m a t r i x i s o f p a r t i c u l a r i m p o r t a n c e i n d e t e r m i n i n g t h e a v a i l a b l e

p h o t o c h e m i c a l r e a c t i o n r o u t e s .

165

CHAPTER 5

EXPERIMENTAL SECTION

166

5 . 1 M a t e r i a l s

A l l monomers w e r e w a s h e d t o r e m o v e i n h i b i t o r s a c c o r d i n g t o

t h e l i t e r a t u r e p r o c e d u r e s 113 a n d d i s t i l l e d u n d e r v a c u u m b e f o r e

u s e . Th e y w e r e s t o r e d a t - 2 0 ° C u n d e r a r g o n u n t i l r e q u i r e d .

A z o b i s i s o b u t y r o n i t r i l e (AIBN) ( M e r c k ) was r e c r y s t a l l i s e d f r o m

a n h y d r o u s m e t h a n o l a n d s t o r e d a t 4°C. M e t a l h e x a c a r b o n y l s

( R i e d e l - d e H aen o r S t r e m ) w e r e u s e d a s s u p p l i e d . T e t r a h y d r o f u r a n

a n d t o l u e n e w e r e r e f l u x e d o v e r l i t h i u m a l u m i n i u m h y d r i d e o r

c a l c i u m h y d r i d e , d i s t i l l e d u n d e r a r g o n , a n d s t o r e d o v e r s o d i u m

w i r e . S o l v e n t s u s e d f o r U V / v i s m e a s u r e m e n t s w e r e a n a l a r g r a d e .

N i t r o g e n o r a r g o n g a s e s w e r e u s e d a s s u p p l i e d f r o m e i t h e r I r i s h

I n d u s t r i a l G a s e s L t d . o r C r y o g a s L t d .

5 . 2 E q u i p m e n t a n d P r o c e d u r e s

5 . 2 . 1 I n f r a r e d a n d UV/visible S p e c t r a l Studies

I n f r a r e d s p e c t r a w e r e r e c o r d e d o n a P e r k i n - E l m e r 983G r a t i o

r e c o r d i n g i n s t r u m e n t , u s i n g a n i n t e r n a l p o l y s t y r e n e s p e c t r u m a s

c a l i b r a t i o n . T h i s m a c h i n e i s f i t t e d w i t h p r e - s a m p l e c h o p p i n g a n d

t h e r e f o r e c a n c o m p e n s a t e f o r s a m p l e e m i s s i o n . P e a k max ima a r e

a c c u r a t e t o ± 3 cm- 1 . A l l monomer c o m p l e x e s w e r e r e c o r d e d a s

N u j o l m u l l s b e t w e e n s o d i u m c h l o r i d e p l a t e s . P o l y m e r c o m p l e x

s p e c t r a w e r e r e c o r d e d a s c a s t f i l m s f r o m c h l o r o f o r m s o l u t i o n on

s o d i u m c h l o r i d e p l a t e s . P o l y m e r f i l m s w e r e c a s t on a s a p p h i r e

s u p p o r t f o r v a r i a b l e t e m p e r a t u r e a n d l o w - t e m p e r a t u r e p h o t o l y s i s

e x p e r i m e n t s , t h e i n t e n s i t y o f t h e c a r b o n y l s t r e t c h i n g

f r e q u e n c i e s c o u l d b e a l t e r e d by c h a n g i n g t h e t h i c k n e s s o f t h e

f i l m . A S p e c a c Model 21000 v a r i a b l e t e m p e r a t u r e s o l i d s s a m p l e

167

a n d a v a r i a b l e t e m p e r a t u r e 10 cm p a t h l e n g t h g a s c e l l , f i t t e d

w i t h a S p e c a c Mode l 2 0100 a u t o m a t i c c o n t r o l u n i t w e r e u t i l i s e d

f o r v a r i a b l e t e m p e r a t u r e i n f r a r e d w o r k . A s c h e m a t i c d i a g r a m o f

t h e v a r i a b l e t e m p e r a t u r e i s shown i n F i g u r e 5 . 1 . The s ame c e l l

was u s e d f o r l o w - t e m p e r a t u r e p h o t o l y s i s e x p e r i m e n t s u s i n g l i q u i d

n i t r o g e n a s t h e c o o l a n t . S a m p l e t e m p e r a t u r e s a r e e s t i m a t e d t o b e

a c c u r a t e t o ± 5°C. U l t r a v i o l e t / v i s i b l e s p e c t r a w e r e r e c o r d e d

e i t h e r on a S h i m a d z u UV240 g r a t i n g s p e c t r o m e t e r ( p e a k p o s i t i o n s

a c c u r a t e t o ± 0 . 5 nm) o r a H e w l e t t - P a c k a r d 8452A d i o d e - a r r a y

s p e c t r o p h o t o m e t e r ( p e a k p o s i t i o n s a c c u r a t e t o ± 2 nm) f i t t e d

w i t h a C h e m s t a t i o n d a t a s t a t i o n . S p e c t r a w e r e r e c o r d e d

i m m e d i a t e l y on d i s s o l u t i o n o f s a m p l e s .

F i g . 5 . 1 S a m p l e h o l d e r u s e d f o r v a r i a b l e

l o w - t e m p e r a t u r e p h o t o l y s i s e x p e r i m e n t s .

t e m p e r a t u r e a n d

(a) sapphire disc(b) disc support(c) liquid nitrogen por t(d) thermocouple(e) outer cell windows (NaCl)(f) vacuum jacket(g) to vacuum(h) path of monitoring IR beam

or photolysis beam.

168

5.2.3 Thermal Analysis

D i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y e x p e r i m e n t s w e r e

c o n d u c t e d on a S t a n t o n R e d c r o f t DSC-700 i n s t r u m e n t . T h e r m o g r a m s

w e r e r e c o r d e d u s i n g c a l c i n e d a - a l u m i n a ( BDH A n a l a R ) a s t h e

r e f e r e n c e m a t e r i a l . S a m p l e c r u c i b l e s w e r e a l u m i n i u m a n d t y p i c a l

s a m p l e w e i g h t s w e r e i n t h e r a n g e 2 - 1 0 mg. S u b - a m b i e n t w o r k was

c o n d u c t e d u s i n g a l i q u i d n i t r o g e n c o l d f i n g e r a t t a c h m e n t . A l l

e x p e r i m e n t s w e r e c a r r i e d o u t u n d e r a n i t r o g e n a t a f l o w r a t e o f

30 cm3/ m i n . A L i n s e i s L6512 c h a r t r e c o r d e r was u s e d t o r e c o r d

t h e o u t p u t . The p e r f o r m a n c e o f t h e i n s t r u m e n t was a s s e s s e d u s i n g

s t a n d a r d s a m p l e s o f p o t a s s i u m n i t r a t e a n d p o t a s s i u m s u l p h a t e .

T e m p e r a t u r e s w e r e f o u n d t o b e a c c u r a t e t o ± 3°C. G l a s s

t r a n s i t i o n t e m p e r a t u r e s w e r e t a k e n a s t h e o n s e t t e m p e r a t u r e o f

t h e h e a t c a p a c i t y c h a n g e . T h e r m o g r a v i m e t r i c a n a l y s i s was

p e r f o r m e d on a S t a n t o n R e d c r o f t T G - 7 5 0 . A p l a t i n u m c r u c i b l e was

u s e d . T y p i c a l s a m p l e w e i g h t s w e r e i n t h e r a n g e 1 - 5 mg. A l l

a n a l y s e s w e r e c a r r i e d o u t u n d e r a n i t r o g e n a t m o s p h e r e a t a f l o w

r a t e o f 20 cm3/ m i n .

5 . 2 . 4 Gel P e r m e a t i o n Chromatography.

Gel p e r m e a t i o n c h r o m a t o g r a p h y (GPC) was c a r r i e d o u t u s i n g a

PL-GEL ( 1 0 pm MIXED 300 X 7 . 5 mm) c o l u m n , a n d a PL-GEL ( 1 0 pm

100A 50 X 7 . 5 mm) p r e - c o l u m n . A 20 p i i n j e c t i o n l o o p was u s e d .

The d e t e c t o r was a W a t e r s R401 D i f f e r e n t i a l R e f r a c t o m e t e r . The

m e t h o d o f U n i v e r s a l C a l i b r a t i o n 76“ was u s e d t o d e t e r m i n e t h e

m o l e c u l a r w e i g h t s o f c o p o l y m e r s o f s t y r e n e a n d 4 - v i n y l p y r i d i n e

( 2 0 / 1 m o l e r a t i o o f s t y r e n e t o 4 - v i n y l p y r i d i n e ) u s i n g

p o l y s t y r e n e s t a n d a r d s ( P o l y m e r L a b o r a t o r i e s L t d . ) . S t a b i l i s e d

169

t e t r a h y d r o f u r a n ( R i e d e l - d e H a en ) was u s e d a s t h e m o b i l e p h a s e

( f l o w r a t e 0 . 4 cm3/ m i n ) , a n d t o l u e n e (BDH A n a l a r ) a s t h e

i n t e r n a l s t a n d a r d t o c o r r e c t f o r d e v i a t i o n s i n f l o w r a t e . The

m o b i l e p h a s e was d e g a s s e d b y f i l t e r i n g t h r o u g h 0 . 5 pm M i l l i p o r e

f i l t e r s u n d e r v a c u u m . S t a n d a r d s a n d s a m p l e s w e r e p r e p a r e d i n THF

a t c o n c e n t r a t i o n s o f 0 . 4% w / v . The d a t a f r o m t h e d e t e c t o r was

a n a l y s e d u s i n g GPC s o f t w a r e ( P o l y m e r L a b o r a t o r i e s L t d . ) on a BBC

m i c r o c o m p u t e r . F i g u r e 5 . 2 s h o ws t h e c a l i b r a t i o n c u r v e o b t a i n e d

f o r t h e p o l y s t y r e n e s t a n d a r d s w i t h w h i c h t h e u nknown s a m p l e s

w e r e c o m p a r e d , a n d T a b l e 5 . 1 g i v e s t h e c o r r e s p o n d i n g

e x p e r i m e n t a l d a t a .

C o p o l y m e r s o f v a r y i n g m o l e c u l a r w e i g h t s w e r e s y n t h e s i s e d by

u s i n g d i f f e r e n t p e r c e n t a g e s o f AIBN i n t h e p o l y m e r i s a t i o n

m i x t u r e . The m o l e c u l a r m a s s e s c a l c u l a t e d h o w e v e r , a r e n o t

c o r r e c t a s t h e s a m p l e s w e r e c o m p a r e d w i t h p o l y s t y r e n e s t a n d a r d s

r a t h e r t h a n p o l y ( s t y r e n e - c o - 4 - v i n y l p y r i d i n e ) s t a n d a r d s . F o r

r e l a t i v e w o r k , h o w e v e r , t h i s m e t h o d p r o v e s q u i t e

s a t i s f a c t o r y 703. GPC r e s u l t s i n d i c a t e d t h a t m o l e c u l a r w e i g h t d i d

c h a n g e a s t h e c o n c e n t r a t i o n o f i n i t i a t o r was v a r i e d . The

c o m p o n e n t w e i g h t s o f mo n ome rs u s e d i n t h e p r e p a r a t i o n o f t h e s e

c o p o l y m e r s a n d t h e c a l c u l a t e d m o l e c u l a r w e i g h t s a n d

d i s t r i b u t i o n s a r e g i v e n i n T a b l e 5 . 2 . C r o s s l i n k e d c o p o l y m e r s

w e r e p r e p a r e d u s i n g d i v i n y l b e n z e n e ( A l d r i c h ) , b u t t h e p o l y m e r s

w e r e i n s o l u b l e , o n l y s w e l l i n g i n s o l v e n t s , a n d s o u s e l e s s f o r

o u r i n t e n d e d a p p l i c a t i o n .

170

Fig. 5.2 GPC calibration curve for polystyrene standards.

3E l u t i o n v o l u m e ( cm )

T a b l e 5 . 1 E x p e r i m e n t a l d a t a f o r a p o l y s t y r e n e c a l i b r a t i o n c u r v e .

E l u t i o n v o l u m e

( cm3 )

M o l e c u l a r W e i g h t ( amu)

S t a n d a r d sL i n e a r F i t

C a l c u l a t e d R a t i o

1 0 . 0 9 1250 1145 1 . 0 9

9 . 5 7 3250 3740 0 . 8 79 . 1 6 9200 9510 0 . 9 78 . 5 6 34500 3 72 66 0 . 9 38 . 3 2 68000 64353 1 . 0 67 . 6 0 4 700 0 0 3 3 1 3 6 8 1 . 4 27 . 0 0 1 0 2 0 0 0 0 1 2 9 8 4 6 6 0 . 7 9

3* T o l u e n e e l u t e d after 1 3 . 9 5 cm

171

T a b l e 5 . 2 The w e i g h t s ( g ) o f t h e m a t e r i a l s u s e d i n t h e s y n t h e s e s

o f p o l y m e r s o f v a r y i n g m o l e c u l a r w e i g h t .

% AIBN S t y r e n e 4 - v p AIBN

( ° C )

Mw

(amu)

Mn

( a mu)

V Mn

4 . 0 0 3 . 0 0 0 0 . 1 5 1 5 . 1 2 6 0 108 1 0 6 0 0 5 6 5 0 1 . 8 8

2 . 0 0 3 . 0 0 0 0 . 1 5 1 5 . 0 6 3 0 113 1 7 2 0 0 8 1 8 0 2 . 1 1

1 . 0 0 3 . 0 0 0 0 . 1 5 1 5 . 0 3 2 0 120 2 6500 1 4 8 8 0 1 . 7 8

0 . 6 6 3 . 0 0 0 0 . 1 5 1 5 . 0 2 1 1 122 3 8 300 1 9 1 5 0 2 . 0 0

0 . 5 0 3 . 0 0 0 0 . 1 5 1 5 . 0 1 5 7 115 4 7 4 0 0 2 8 20 0 1 . 8 8

0 . 4 0 3 . 0 0 0 0 . 1 5 1 5 . 0 1 2 6 122 5 1 10 0 2 5 8 0 0 1 . 98

0 . 3 3 3 . 0 0 0 0 . 1 5 1 5 . 0 1 0 5 126 67500 3 0 1 0 0 2 . 2 4

0 . 2 5 3 . 0 0 0 0 . 1 5 1 5 . 0 0 7 9 122 7 0 900 3 1 4 0 0 2 . 2 5

0 . 2 0 3 . 0 0 0 0 . 1 5 1 5 . 0 0 6 4 125 99800 4 72 00 2 . 1 1

0 . 1 0 5 . 0 0 0 0 . 2 5 2 4 . 0 0 5 2 128 1 6 2 0 0 0 7 0 2 0 0 2 . 3 1

0 . 0 5 5 . 0 0 0 0 . 2 5 2 4 . 0 0 2 6 132 2 0 4 0 0 0 8 67 0 0 2 . 3 6

Tg = g l a s s t r a n s i t i o n t e m p e r a t u r e ( a D e t e r m i n e d b y DSC) .

AIBN = a z o b i s i s o b u t y r o n i t r i l e

4 - v p = 4 - v i n y l p y r i d i n e

M. = w e i g h t a v e r a g e m o l e c u l a r w e i g h t wM n = n u m b e r a v e r a g e m o l e c u l a r w e i g h t

172

5.2.5 Atomic Absorption Spectroscopy (AAS).An Instrumentation-Laboratories IL-AA/AE 357 instrument was

utilised for metal determinations. Chromium, molybdenum and tungsten standards were prepared over the linear range stated in the Instrumentation-Laboratories manual by serial dilution of atomic absorptions standards (Spectrosol BDH). All of the solutions for atomic absorption measurements were prepared in distilled water which had been further purified using the Milli-Q water purification system. The glassware used was soaked in 1.6 M nitric acid and thoroughly rinsed with Milli-Q waterprior to use. A fuel rich N O-Acetylene flame (cone 2 cm high)

2oand an aspiration rate of 6 cm /minute was used. Other

instrumental conditions are available in the IL-AA/AE 357 instrument manual. The experimental data and correlations for the standard solutions are given below in Tables 5.3a and 5.3b.

Table 5.3a Atomic Absorption Standards.

Metal Linear Range (ppm)

Correlation Intercept Si ope

Cr 0 - 5 0.996 -2 . lE-3±4.8E-3 2.4E-2±1.7E-3Mo 0 - 6 0 0.999 -1.3E-2±1.2E-2 1.lE-2±2.8E-4W 0 - 500 0.999 -9.9E-4±2.8E-3 3.4E-4±5.5E-6

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Table 5.3b Experimental results for atomic absorption standards.

Cr conc. (ppm)

Absorbance (377.9nm)

Mo conc. (ppm)

Absorbance (313.3nm)

W conc. (ppm)

Absorbance (255.lnm)

0.2 0.004 1.0 0.008 50 0.0151.0 0.024 5.0 0.047 75 0.0232.0 0.040 10 0.095 100 0.0353.0 0.069 20 0.190 150 0.0524.0 0.096 30 0.318 200 0.0675.0 0.118 40 0.419 250 0.084

- - 50 0.549 300 0.100- - 60 0.648 350 0.118- - - - 400 0.143- - - - 500 0.168

Readings were taken against a Hilli-Q water blank (A>0.000).

Polymer samples were digested in 6 cm3 concentrated sulphuric acid (May and Baker Analar Grade) with gentle heating. Following acid digestion, the samples were cooled and 3 cm3 of hydrogen peroxide (Riedel-de Haen 70 % v/v) added carefully. After further heating, the clear solutions were cooled to room temperature and diluted to the 100 cm3 volumetric mark with Milli-Q water. Another set of samples were heated under vacuum at 180 °C to produced the decarbonylated polymers. Infrared spectroscopy confirmed the absence of carbonyl stretching bands. These were then digested as described above. The absorbance of the polymer samples were read against a digested unmetallated polymer blank. Enough polymer sample was weighed to give an

174

absorbance within the linear range for that metal, based on the theoretical metal content. Table 5.4 shows the results for the determination of the metal content following thermal decarbonylation.

Table 5.4 Determination of metal content of polymers after thermal decarbonylation by AAS.

Carbonylated DecarbonylatedPolymerSample weight

( g )Abs. M

(ppm)weight

( g )Abs. M

(ppm)%M

P[styrene- W(CO) (4-vp)]b .2006 .043 127.0 .2013 .037 111.8 | 88P[styrene- Cr(CO) (4-vp)] .0253 .112 4.8 .0255 .097 4.1 ! 86P[styrene- Mo(CO) ]9 .1021 .347 32.7 .1038 .322 30.4 93P[styrene- M(CO) (2-vp)]5 .2011 .042 124.4 .2023 .038 112.0 90P[styrene-W(CO)4(Vbipy)] .2009 .041 121.8 .2041 .039 116.9 96

P[styrene-W(CO)5(4-vp)] .1002 .049 145.2 .0973 .041 123.4 82(5/1 mol ratio)

P[4-vp- W(CO) (4-vp)] .1021 .022 65.3 .1008 .019 59.4 91P[MA- W(CO) (4-vp)]t> .1592 .036 106.6 .1612 .032 94.9 89P[styrene- p-SDPP]-W(CO)

5.1242 .021 63.5 .1204 .020 59.7 94

P[styrene-p-SDPP]-Cr(C0)5 .0125 .043 1.9 .0137 .039 1.7 90P[styrene- p-SDPP]-Mo (C0)5 .1012 .236 22.6 .0987 .216 20.8 92

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N o t e s on T a b l e 5.4All o o p o l y a e r a c o n t a i n 20/1 mole ratio of metal carbonyl to

m o n o m e r u n l e s s o t h e r w i s e stated.3All w e i g t h s of p o l y m e r s are per 100 cm .

Abs » a b s o r b a n c e , M ■ m e t a l , %M refers to the percentage metalr e m a i n i n g f o l l o w i n g t h e r m a l decarbonylatlon.

vp ■ v l n y l p y r i d i n e , HA ■ methyl aorylate,P - S D P P “ p a r a - s t y r y l d i p h e n y l p h o s p h i n e

V b i p y ■ 4 - v i n y 1 - 4 ' - me t h y 1 - 2 , 2 ’-bi pyr idyl .

5.2.6 Photolysis ExperimentsPreparative photolyses were performed using an Applied

Photophysics 400 W medium pressure mercury vapour lamp. The lamp was housed in a double-walled quartz jacket through which water was circulated to prevent the lamp heating the photolysis solution. An Oriel 100 W short-arc mercury lamp was employed in low temperature photolyses experiments. The light was firstly collimated, passed through an infrared filter containing Milli-Q water, and finally through the sodium chloride windows of the variable temperature cell.

5.2.7 Flash Photolysis of W(CO)g Toluene Solutions Containing Pyridine Ligands.Samples for flash photolysis experiments were prepared in

anhydrous toluene (Aldrich Sureseal). Toluene solutions containing tungsten hexacarbonyl (1.14 X 10“7M,e = 1.41 X 106 mol_1dm3cm-1 at 355 nm) and pyridine (Aldrich Gold Label) were degassed by three freeze-pump-thaw cycles, followed by a liquid pumping phase, and then placed under one atmosphere of argon. Polymer samples containing the required

176

c o n c e n t r a t i o n o f p y r i d i n e ( b a s e d on % N d e t e r m i n e d by

m i c r o a n a l y s i s ) a n d t h e d e s i r e d a m o u n t o f h e x a c a r b o n y l

( 1 . 1 4 X 1 0 " 7M) w e r e p r e p a r e d i n t o l u e n e a n d d e g a s s e d a s a b o v e .

A l l p o l y m e r s w e r e d r i e d u n d e r v a c u u m p r i o r t o u s e . T a b l e 5 . 5

g i v e s t h e w e i g h t s o f m o n o m e r i c a n d p o l y m e r i c p y r i d i n e u s e d i n

t h e s t u d y .

T a b l e 5 . 5 W e i g h t s o f s a m p l e s u s e d f o r f l a s h p h o t o l y s i s s t u d i e s .

W e i g h t ( g ) / 10 cm3 T o l u e n e

C o n c e n t r a t i o n s ( E - 2 H)

S a m p l e % Na 0 . 5 1 . 0 2 . 0 3 . 0 4 . 0

P y r i d i n e P o l y m e r 1 0 / 1

P o l y m e r 5 / 1

1 . 6 9

2 . 6 0

0 . 0 0 3 6

0 . 0 4 1 20 . 0 2 6 9

0 . 0 0 8 50 . 0 8 2 8

0 . 0 5 3 9

0 . 0 1 7 20 . 1 6 5 7

0 . 1 0 7 6

0 . 0 2 5 80 . 2 4 8 5

0 . 1 6 3 4

0 . 0 3 2 4

0 . 3 3 1 4

0 . 2 1 5 2

D e t e r m i n e d by m i oroanal y a i e , UCD N i o r o a n a l y t i c a l Lab, D u b l i n .

A s c h e m a t i c d i a g r a m o f t h e f l a s h p h o t o l y s i s i n s t r u m e n t a t i o n

i s shown i n F i g u r e 5 . 3 . The e x c i t a t i o n s o u r c e i s a Q - s w i t c h e d

Nd-YAG ( n e o d y n i u m d o p e d y t t r i u m a l u m i n i u m g a r n e t ) l a s e r

( S p e c t r o n L a s e r S y s t e m s ) , w h i c h o p e r a t e s a t 1 0 6 4 nm b u t c a n b e

f r e q u e n c y d o u b l e d o r t r i p l e d o r q u a d r u p l e d t o g e n e r a t e a s e c o n d ,

t h i r d , o r f o u r t h h a r m o n i c f r e q u e n c y a t 5 3 2 , 3 5 5 , a n d 266 nm

r e s p e c t i v e l y . The p o w e r o f t h e l a s e r p u l s e c a n b e v a r i e d by

a p p l y i n g d i f f e r e n t v o l t a g e s a c r o s s t h e a m p l i f i e r f l a s h t u b e . At

355 nm, t h e p o w e r o u t p u t was t y p i c a l l y 3 0 - 4 0 mJ . T h e p u l s e t i m e

v a r i e s f r o m 5 t o 10 n s . The c i r c u l a r l a s e r p u l s e ( c a . 4 mm i n

d i a m e t e r ) i s d i r e c t e d v i a t w o P e l l i n - B r o c a p r i s m s o n t o t h e

177

sample cuvette. A power meter, placed between the the second prism and sample holder, is used to trigger the oscilloscope and to measure pulse to pulse variation (this was estimated to be ± 5% at most in these experiments, and no correction was made for power variations. The monitoring light source was an Applied Photophysics 40804 air cooled 275 W Xenon arc lamp used at right angles to the laser beam. A UV filter (X > 400 nm or X > 345 nm) was placed between the monitoring source and the sample to prevent photolysis of the sample by the monitoring beam. The beam passes through the sample cell and is focused via a circular quartz lens onto the slit of a f/3.4 Applied Photophysics monochromator. The light detector is a Hamamatzu5-stage photomultiplier which was operated at 850 volts. The signal output was connected via a variable load resistor to the transient analyser, a Phillips PM 3311 oscilloscope. The oscilloscope is partially controlled by a BBC microcomputer connected by an Acorn IEEE-488 computer interface.

An experiment is one of monitoring absorbance changes. Laser photolysis produces a transient species whose absorbance is recorded as a function of time. Initially IQ, the amount of monitoring light being transmitted through the solution before the laser flash is measured. This is achieved by recording the voltage corresponding to that light detected by the photomultiplier tube when the monitoring source shutter is open. I is directly proportional to this voltage. When recording transient data, the monitoring shutter is opened and the laser

178

f i r e d . The l a s e r beam p a s s e s t h r o u g h t h e p o w e r m e t e r , t r i g g e r i n g

t h e o s c i l l o s c o p e , a n d h i t s t h e s a m p l e c u v e t t e p r o d u c i n g a

t r a n s i e n t s p e c i e s . T h e m o n i t o r i n g beam t r a v e r s e s t h e r e g i o n o f

t h e c u v e t t e w h e r e t h e l a s e r p a s s e d . The o s c i l l o s c o p e r e c o r d s t h e

c h a n g e i n v o l t a g e w i t h t i m e f r o m t h e p h o t o m u l t i p l i e r t u b e ,

c o r r e s p o n d i n g t o a c h a n g e i n a b s o r b a n c e w i t h t i m e a t t h e

m o n i t o r i n g w a v e l e n g t h . T h e o s c i l l o s c o p e s t o r e s t h e t r a c e a n d t h e

t r a n s i e n t d a t a c a n b e s t o r e d on f l o p p y d i s c f o r a n a l y s i s . The

s t o r e d d a t a c a n b e u s e d t o c a l c u l a t e I fc, t h e a m o u n t o f l i g h t

b e i n g t r a n s m i t t e d a t a n y t i m e t . An a b s o r b a n c e s p e c t r u m o f t h e

t r a n s i e n t s p e c i e s i s o b t a i n e d by r e c o r d i n g t r a n s i e n t s i g n a l s a t

d i f f e r e n t m o n i t o r i n g w a v e l e n g t h s . The a b s o r b a n c e r e a d i n g s c a n

t h e n b e c a l c u l a t e d a t a n y t i m e a f t e r t h e f l a s h . The o s c i l l o s c o p e

i s s e t a t a d e l a y t o e n a b l e t h e a b s o r b a n c e ( c o r r e s p o n d i n g t o t h e

a b s o r b a n c e o f t h e p a r e n t m a t e r i a l a t t h a t w a v e l e n g t h ) t o b e

r e c o r d e d b e f o r e t h e l a s e r p u l s e . A t r a n s i e n t d i f f e r e n c e s p e c t r u m

i s t h e n o b t a i n e d f r o m a p l o t o f a b s o r b a n c e v e r s u s w a v e l e n g t h .

F o r A r r h e n i u s e x p e r i m e n t s , t h e s a m p l e c e l l was i m m e r s e d i n

a t h e r m o s t a t e d w a t e r b a t h a n d a l l o w e d t o e q u i l i b r a t e d f o r 20

m i n u t e s . I q was m e a s u r e d a t t h e m o n i t o r i n g w a v e l e n g t h

(X = 395 nm) a n d t h e s y s t e m r e a d i e d f o r a n a l y s i s p r i o r t o t h e

s a m p l e b e i n g h e a t e d s o t h a t t h e t r a n s i e n t d a t a c o u l d b e r e c o r d e d

i m m e d i a t e l y on r e m o v i n g t h e c e l l f r o m t h e w a t e r b a t h . The s a m p l e

was h e a t e d i n c r e m e n t a l l y f r o m room t e m p e r a t u r e t o 50°C, a

t r a n s i e n t b e i n g r e c o r d e d f o r a n a l y s i s e v e r y 5°C.

179

Fig. 5.3 Schematic diagram of the laser flash photolysis system.

A laser G monochromatorB prisms H photomultiplierC power meter I computerD sample cell housing J IEEE interfaceE xenon arc lamp K oscilloscopeF Xenon lamp power supply

180

5 . 3 S y n t h e s i s o f Monomer C o m p l e x e s

5 . 3 . 1 S y n t h e s i s o f M(CO)^(vinylpyridine).

T h e c o m p l e x e s w e r e p r e p a r e d v i a t h e c o r r e s p o n d i n g

t e t r a h y d r o f u r a n c o m p l e x a c c o r d i n g t o t h e l i t e r a t u r e

p r o c e d u r e s 17' 24 , 6 9 .

M( C0 ) 6 fHF—* M(CO)5 (THF) — > M(CO)s ( v p ) ( 1 )

A t y p i c a l p r e p a r a t i o n i n v o l v e d t h e p h o t o l y s i s o f t h e p a r e n t

h e x a c a r b o n y l ( 1 . 0 g ) i n f r e s h l y d i s t i l l e d THF ( 2 0 0 cm3 ) a t room

t e m p e r a t u r e f o r a b o u t f o u r h o u r s . The p h o t o l y s i s s o l u t i o n was

c o n t i n u o u s l y p u r g e d w i t h a s t r e a m o f n i t r o g e n t o a i d t h e r e m o v a l

o f CO a n d m a i n t a i n a n i n e r t a t m o s p h e r e o v e r t h e p h o t o l y s i s

s o l u t i o n . F o l l o w i n g t h e p h o t o l y s i s , t h e r e s u l t i n g c l e a r y e l l o w

s o l u t i o n was a d d e d t o a t w o m o l a r e x c e s s o f t h e d e s i r e d

v i n y l p y r i d i n e u n d e r n i t r o g e n . The THF was r e m o v e d b y r o t a r y

e v a p o r a t i o n . The c r u d e p r o d u c t was r e c r y s t a l l i s e d f r o m d e g a s s e d

e t h a n o l - c h l o r o f o r m t o y i e l d b r i g h t y e l l o w c r y s t a l s . Y i e l d s w e r e

t y p i c a l l y 70 %. T h e c o m p l e x e s w e r e pumped u n d e r v a c u u m t o r e m o v e

a n y t r a c e s o f s o l v e n t a n d m e t a l h e x a c a r b o n y l . T h e p u r i t y o f t h e

c o m p l e x e s was c o n f i r m e d b y i n f r a r e d s p e c t r o s c o p y . T h e i n f r a r e d

a n d U V / v i s d a t a a g r e e d w i t h t h a t a l r e a d y p u b l i s h e d 28' 6 9 . The

c o m p l e x e s a r e s o l u b l e i n c h l o r i n a t e d s o l v e n t s , a l c o h o l s ,

e t h e r , a n d s l i g h t l y s o l u b l e i n h y d r o c a r b o n s . A l t h o u g h a l l t h e

c o m p l e x e s w e r e h a n d l e d a s a i r s e n s i t i v e , c o m p l e x e s o f c h r o m i u m

a n d t u n g s t e n a n d 4 - v i n y l p y r i d i n e show c o n s i d e r a b l e s t a b i l i t y

e v e n i n a e r a t e d s o l u t i o n . C o m p l e x e s o f m o l y b d e n u m a r e l e s s

s t a b l e a n d d e c o m p o s e i n s o l u t i o n e v e n when d e g a s s e d . T h o s e

181

c o m p l e x e s o f 2 - v i n y l p y r i d i n e a r e much l e s s s t a b l e , d e c o m p o s i n g

r a p i d l y i n s o l u t i o n e v e n when d e g a s s e d . [Mo(CO) ( 2 - v p ) ] c o u l d

n o t b e i s o l a t e d f r o m r e a c t i o n 1 , p r e s u m a b l y b e c a u s e o f i t ' s

t e n d e n c y t o d i s s o c i a t e . I n g e n e r a l , t h e s t a b i l i t y o f t h e

c o m p l e x e s i s i n t h e o r d e r W > Cr >> Mo a n d 4 - v p > 2 - v p . The

d e c r e a s e d s t a b i l i t y o f t h e 2 - v i n y l p y r i d i n e c o m p l e x e s i s

a t t r i b u t e d t o s t e r i c i n t e r a c t i o n o f t h e M(CO) g r o u p a n d t h e5

v i n y l g r o u p 29 . No e v i d e n c e was f o u n d f o r o t h e r c o m p l e x e s s u c h a s

[M(CO) ( v p ) ] , [M(CO) (p - vp ) M( CO) ] , o r [ (r)2- vp ) M(CO) ] ,4 2 5 5 5

i n d i c a t i n g t h a t t h e s e a r e m i n o r p r o d u c t s a t t h e v e r y b e s t .

(W(CO) ( 4 - v p ) A n a l . C a l c d . : C 3 3 . 5 9 , H 1 . 6 4 , N 3 . 2 6 . P o u n d :5C 3 2 . 8 2 , H 1 . 6 1 , N 3 . 1 9 . W(CO) ( 2 - v p ) A n a l . C a l c d . : C 3 3 . 5 9 ,5H 1 . 6 4 , N 3 . 2 6 . F o u n d : C 3 0 . 5 8 , H 1 . 4 5 , N 3 . 1 8 ) . I n f r a r e d

s p e c t r o s c o p i c d a t a w e r e p r e v i o u s l y g i v e n i n T a b l e 2 . 1 .

5 . 3 . 2 P r e p a r a t i o n o f M ( C O ) 4 (4-vinyl-4'-methyl- 2 , 2 ' -bipyridyl ) .

4 - v i n y l - 4 ' - m e t h y l - 2 , 2 ' - b i p y r i d y l was p r e p a r e d a c c o r d i n g t o

t h e m e t h o d o f G ho s h a n d S p i r o 67b. [M(CO) ( T H F ) ] was p r e p a r e d a s5d e s c r i b e d a b o v e a n d r e a c t e d w i t h a m o l a r e q u i v a l e n t o f t h e

b i p y r i d y l i n d r y THF u n d e r n i t r o g e n . A d e e p r e d s o l u t i o n was

f o r m e d i m m e d i a t e l y . The THF was r e m o v e d u n d e r v acu u m a n d t h e

c r u d e p r o d u c t was r e c r y s t a l l i s e d f r o m a d e g a s s e d a c e t o n e - t o l u e n e

m i x t u r e t o y i e l d m a r o o n c r y s t a l s . The p r o d u c t was w a s h e d w i t h

h e x a n e a n d d r i e d u n d e r v a c u u m . P u r i t y was c o n f i r m e d by i n f r a r e d

s p e c t r o s c o p y . The s p e c t r o s c o p i c d a t a a g r e e d w e l l w i t h p r e v i o u s l y

r e p o r t e d s t u d i e s on s i m i l a r c i s - [ M ( C O ) ( b i p y ) ] c o m p l e x e s4A l l c o m p l e x e s w e r e t r e a t e d a s a i r s e n s i t i v e a n d w e r e s t o r e d

182

under argon. The tetracarbonyls showed varying degrees of stability and readily decomposed on recrystallisation even in degassed solutions. In general the stabilities were in the order Mo > W > Cr. (W(CO)4(Vbipy) Anal.Calcd.: C 41.48, H 2.46,N 5.68, Found: C 41.27, H 2.45, N 5.84).

Table 5.6 Component weights for synthesis of monomer complexes.

Compl ex 4 - v p 2 - v p V b i p y

m ( c o ) 6

Cr Mo W

Cr(CO) ( 4 - v p )b 0 . 9 5 6 0 - - 1 . 0 0 0 4 - -

Mo(CO) ( 4 - v p )5

0 . 6 7 9 0 - - - 0 . 8 5 2 5 -

W(CO) ( 4 - v p )b 0 . 5 9 8 0 - - - - 1 . 0 0 0 0

Cr (CO) ( 2 - v p )t>- 0 . 4 8 7 0 - 0 . 5 0 9 6 - -

W(CO) ( 2 - v p )b - 0 . 6 0 1 0 - - - 1 . 0 0 0 0

C r ( C O ) ^ ( V b i p y ) - - 0 . 1 5 0 0 0 . 1 6 8 2 - -

Mo(CO) ( V b i p y ) - - 0 . 1 2 5 0 - 0 . 1 6 8 2 -

W ( C O ) ^ ( V b i p y ) - - 0 . 2 0 0 0 - - 0 . 3 5 8 7

All w e i g h t s in grams.

183

5 . 3 . 3 S y n t h e s i s o f p-Styryldiphenylphosphine.3 8 * , ,

The m e t h o d o f R a b i n o w i t z a n d M a r c u s , w i t h some s l i g h t

m o d i f i c a t i o n s t o t h e p u b l i s h e d p r o c e d u r e , was u s e d t o p r e p a r e

p - s t y r y l d i p h e n y l p h o s p h i n e ( p - SD PP ) i n g o o d y i e l d . T h e s y n t h e s i s

i n v o l v e d t h e r e a c t i o n p - s t y r y l m a g n e s i u m b r o m i d e w i t h

c h i o r o d i p h e n y l p h o s p h i n e a t 0°C u s i n g i n v e r s e a d d i t i o n . The

o r g a n o m e t a l l o i d h a l i d e i s p r e p a r e d b y G r i g n a r d s y n t h e s i s a n d

a d d e d t o a s o l u t i o n o f t h e p h o s p h i n e . D i r e c t a d d i t i o n o f t h e

p h o s p h i n e t o t h e G r i g n a r d r e a g e n t was r e p o r t e d t o r e s u l t i n h i g h

d e g r e e s o f p o l y m e r i s a t i o n .

Materials

4 - b r o m o s t y r e n e ( A l d r i c h ) was w a s h e d w i t h a q u e o u s 5% NaOH

(3X) a n d t h e n w i t h d i s t i l l e d w a t e r ( 3 X ) , a n d d r i e d o v e r

m a g n e s i u m s u l p h a t e . I t was t h e n d i s t i l l e d u n d e r r e d u c e d

p r e s s u r e , d e g a s s e d u n d e r a s t r e a m o f a r g o n a n d s t o r e d a t - 2 0 ° C

u n t i l r e q u i r e d . C h i o r o d i p h e n y l p h o s p h i n e ( A l d r i c h ) wa s d i s t i l l e d

u n d e r v acu um a n d s t o r e d u n d e r a r g o n o v e r t y p e A4 m o l e c u l a r s i e v e

a t 4°C. T e t r a h y d r o f u r a n was d i s t i l l e d u n d e r a r g o n f r o m l i t h i u m

a l u m i n i u m h y d r i d e a n d s t o r e d o v e r s o d i u m w i r e . M a g n e s i u m

t u r n i n g s ( R i e d e l - d e H a e n ) a n d e t h y l b r o m i d e (BDH) w e r e u s e d a s

s u p p l i e d .

P r o c e d u r e

A d r y 250 cm3 t h r e e - n e c k e d r o u n d b o t t o m e d f l a s k ( r b f ) was

f i t t e d w i t h a n a r g o n i n l e t , t h e r m o m e t e r , p r e s s u r e e q u a l i s i n g

d r o p p i n g f u n n e l , a n d a Y - t u b e t o w h i c h was a t t a c h e d a r e f l u x

c o n d e n s e r a n d C a C l 2 d r y i n g t u b e . The v e s s e l was p u r g e d w i t h a

184

s t r e a m o f a r g o n f o r t e n m i n u t e s a n d m a i n t a i n e d a t a p o s i t i v e

a r g o n p r e s s u r e t h r o u g h o u t t h e r e a c t i o n . M a g n e s i u m t u r n i n g s

( 5 . 0 g , 0 . 2 0 6 m o l e ) w e r e t h e n a d d e d v i a a s o l i d s a d d i t i o n f u n n e l

u n d e r a r g o n a n d t h e f l a s k was c h a r g e d w i t h 40 cm3 o f f r e s h l y -

d i s t i l l e d THF. The s u s p e n s i o n was s t i r r e d f o r 10 m i n u t e s w h i l e

p u r g i n g w i t h a s t r e a m o f a r g o n . E t h y l b r o m i d e ( 0 . 5 cm3 ) was

a d d e d v i a a s y r i n g e t o i n i t i a t e t h e r e a c t i o n . T h e t e m p e r a t u r e

r o s e t o 4 0 ° C . The f l a s k was p l a c e d i n a n i c e - b a t h a n d

4 - b r o m o s t y r e n e ( 1 8 . 8 3 g, 0.103 m o l e ) i n 50 cm3 o f THF was a d d e d

d r o p w i s e v i a t h e d r o p p i n g f u n n e l w i t h s t i r r i n g o v e r 0 . 5 h o u r ,

t h e t e m p e r a t u r e n e v e r b e i n g a l l o w e d t o e x c e e d 40°C. T h e r e a c t i o n

was e x o t h e r m i c a n d p r o c e e d e d v i g o r o u s l y , c a r e f u l a d d i t i o n b e i n g

n e e d e d t o m a i n t a i n t h e t e m p e r a t u r e a t a b o u t 40°C. A f u r t h e r

20 cm3 o f THF was a d d e d a n d t h e r e s u l t i n g muddy G r i g n a r d r e a g e n t

was s t i r r e d f o r a f u r t h e r 45 m i n u t e s a t room t e m p e r a t u r e when

a d d i t i o n was c o m p l e t e . D r o p p i n g a n e x t r a c t i n t o m e t h a n o l

r e v e a l e d t h a t some p o l y m e r h a d f o r m e d a t t h i s s t a g e . T h e r e a g e n t

was f i l t e r e d u n d e r a r g o n u s i n g a n o n - l i n e f i l t e r t o r e m o v e a ny

u n r e a c t e d m a g n e s i u m a n d p r e c i p i t a t e d m a g n e s i u m b r o m i d e f o r m e d i n

t h e r e a c t i o n .

A d r y 250 cm3 t h r e e - n e c k e d r b f was e q u i p p e d w i t h a n a r g o n

i n l e t , t h e r m o m e t e r , t e f l o n c o a t e d m a g n e t i c s t i r r i n g b a r , a n d a

r u b b e r s e p t u m . The v e s s e l was f l u s h e d w i t h a s t r e a m o f a r g o n a nd

c h i o r o d i p h e n y l p h o s p h i n e ( 1 6 . 1 2 g , 0 . 0 7 3 m o l e ) i n 40 cm3 THF was

a d d e d v i a s y r i n g e . The s o l u t i o n was c o o l e d t o l e s s t h a n 0°C

u s i n g a n a c e t o n e s l u s h b a t h . The p h o s p h i n e was d e g a s s e d u n d e r a

185

s t r e a m o f a r g o n a n d a l l o w e d t o e q u i l i b r a t e f o r 15 m i n u t e s w i t h

s t i r r i n g . The G r i g n a r d r e a g e n t was a d d e d v e r y g r a d u a l l y o v e r 30

m i n u t e s v i a a n a i r t i g h t s y r i n g e , t h e t e m p e r a t u r e b e i n g

m a i n t a i n e d a r o u n d 0°C. A f t e r a d d i t i o n o f t h e G r i g n a r d was

c o m p l e t e , t h e b r o w n s o l u t i o n was a l l o w e d t o warm t o room

t e m p e r a t u r e a n d s t i r r e d f o r a f u r t h e r 30 m i n u t e s . T h e s o l u t i o n

was p o u r e d i n t o 100 cm3 o f a n a q u e o u s s o l u t i o n o f ammonium

c h l o r i d e ( R i e d e l - d e H a e n ) ( 1 5 g i n 100 cm3 d i s t i l l e d w a t e r ) w i t h

s t i r r i n g t o d e c o m p o s e a n y u n r e a c t e d G r i g n a r d r e a g e n t . T h i s was

t h e n e x t r a c t e d w i t h THP. The THF e x t r a c t s w e r e c o m b i n e d a n d

f i l t e r e d t h r o u g h a b e d o f s i l i c a g e l ( M e r c k ) a n d d r i e d o v e r

m a g n e s i u m s u l p h a t e o v e r n i g h t . The s o l u t i o n was r e d u c e d t o a

v o l u m e o f a b o u t 20 cm3 b y r o t a r y e v a p o r a t i o n a n d a n y p o l y m e r was

p r e c i p i t a t e d (3X) i n p e t r o l e u m e t h e r ( 6 0 0 cm ) . T h e e t h e r was

f i l t e r e d t h r o u g h s i n t e r e d g l a s s a n d t h e s o l v e n t r e m o v e d u n d e r

v ac uu m t o y i e l d a y e l l o w o i l w i t h some w h i t e s o l i d . On a d d i t i o n

o f e t h a n o l , t h e p r o d u c t d r o p p e d o u t o f s o l u t i o n . T h e c r u d e

p r o d u c t was r e c r y s t a l l i s e d f r o m e t h a n o l , a n d t h e r e s u l t i n g

c r y s t a l s w e r e c o l l e c t e d on s i n t e r e d g l a s s , w a s h e d w i t h c o l d

e t h a n o l , a n d d r i e d u n d e r v a cu u m t o y i e l d 1 4 . 9 1 g ( 7 0 % y i e l d ) o f

w h i t e c r y s t a l s . The p r o d u c t c o u l d b e f u r t h e r p u r i f i e d by

c h r o m a t o g r a p h y on s i l i c a . E l u t i o n was f i r s t w i t h

c h l o r o f o r m : p e t r o l e u m e t h e r 4 0 - 6 0 ° C t o r e m o v e p o l y m e r i m p u r i t i e s ,

a n d t h e n w i t h p e t r o l e u m e t h e r . ( A n a l . C a l c d . : P 1 0 . 7 4 , F o u n d :

P 1 1 . 0 6 ; mp 7 6 - 7 7 ° C , L i t . v a l u e 7 7 - 7 8 ° C ; IR ( K B r ) : 1 62 1 ( C =C ) ,

1 42 8 ( P - P h ) , 837 ( d i s u b . a r o m a t i c ) , 7 4 5 , 695 ( m o n o s u b . a r o m a t i c )

cm- 1 . aH NMR (CDCl3 , 1% TMS, 60 MHz): c h e m i c a l s h i f t s (6 i n ppm)

186

a n d c o u p l i n g c o n s t a n t s ( J i n Hz) f o r v i n y l i c H : H^ 6 . 3 8 ( 1 6 . 0 ,

9 . 8 ) , H 5 . 1 6 ( 1 0 . 2 , 1 . 8 ) , H 5 . 6 0 ( 1 6 . 0 , 1 . 8 ) ; a r o m a t i c H2 37 . 1 - 7 . 5 pp m) .

A t t e m p t s t o p r e p a r e m e t a l c a r b o n y l c o m p l e x e s o f p -SDPP v i a

t h e p h o t o c h e m i c a l l y p r o d u c e d [M(CO) (THF) ] a s p r e v i o u s l y5

d e s c r i b e d i n s e c t i o n 5 . 3 . 1 , w e r e u n s u c c e s s f u l . Low y i e l d s o f t h e

d e s i r e d monomer m e t a l c a r b o n y l c o m p l e x e s c o u l d o n l y b e o b t a i n e d ,

c o n s i d e r a b l e a m o u n t s o f p o l y m e r b e i n g f o r m e d i n a l l c a s e s .

5 . 4 P r e p a r a t i o n o f P o l y m e r s a n d P o l y m e r - B o u n d M e t a l C a r b o n y l s

The p o l y m e r s w e r e p r e p a r e d b y a z o b i s i s o b u t y r o n i t r i 1e (AIBN)

i n i t i a t e d f r e e - r a d i c a l p o l y m e r i s a t i o n i n t h e a b s e n c e o f

s o l v e n t . ( C o p o l y m e r s o f a - m e t h y l s t y r e n e w e r e p r e p a r e d by a n i o n i c

p o l y m e r i s a t i o n a n d a r e d i s c u s s e d l a t e r ) . P o l y m e r - b o u n d m e t a l

c a r b o n y l s w e r e p r e p a r e d e i t h e r b y r e a c t i n g p h o t o g e n e r a t e d

[M(CO) ( TH F) ] w i t h p r e f o r m e d c o p o l y m e r s c o n t a i n i n g p e n d a n t s i t e s5

i n a 1 : 1 m o l e r a t i o , o r b y c o p o l y m e r i s a t i o n o f t h e m e t a l

c a r b o n y l f u n c t i o n a l i s e d mo n o m e r s w i t h s u i t a b l e c o m o n o m e r s .

T y p i c a l l y , t h e m i x t u r e s o f mo n o m e r s a n d i n i t i a t o r (2% w/w)

w e r e d e g a s s e d by p u r g i n g t h e s o l u t i o n w i t h a s t r e a m o f n i t r o g e n

f o r 10 m i n u t e s . P o l y m e r i s a t i o n s w e r e c a r r i e d o u t b y h e a t i n g a t

7 5 - 8 5 ° C f o r 1 - 2 h o u r s u n d e r a n i t r o g e n a t m o s p h e r e . I n t h e c a s e

o f c o p o l y m e r s o f s t y r e n e a n d m e t h y l m e t h a c r y l a t e , c o l o u r l e s s

g l a s s - l i k e p o l y m e r s r e s u l t e d w h i l e t h o s e o f e t h y l a n d m e t h y l

187

a c r y l a t e w e r e r u b b e r y i n n a t u r e . The c o p o l y m e r s w e r e p u r i f i e d by

r e p e a t e d p r e c i p i t a t i o n f r o m c h l o r o f o r m s o l u t i o n b y p e t r o l e u m

e t h e r 4 0 - 6 0 ° C ( t h e minimum v o l u m e o f c h l o r o f o r m r e q u i r e d t o

d i s s o l v e t h e p o l y m e r was u s e d a n d t h e r e s u l t i n g s o l u t i o n was

a d d e d d r o p w i s e i n t o a l a r g e v o l u m e o f p e t . e t h e r ( a b o u t 800 cm )

w i t h v i g o r o u s s t i r r i n g ) . The p o l y m e r s w e r e c o l l e c t e d on s i n t e r e d

g l a s s a n d w a s h e d w i t h p e t r o l e u m e t h e r o f e t h a n o l . P o l y m e r s o f

s t y r e n e a n d m e t h y l m e t h a c r y l a t e w e r e i s o l a t e d a s f l o c u l e n t

p o w d e r s , w h i l e t h o s e o f t h e a c r y l a t e s w e r e o b t a i n e d a s r u b b e r y

s o l i d s . A l l p o l y m e r i s a t i o n s p r o c e e d e d i n g o o d y i e l d ( 8 0 - 9 0 % ) .

Th e y w e r e d r i e d u n d e r v a c u u m a t 60°C f o r 24 h o u r s . T h o s e

c o p o l y m e r s o f t h e a c r y l a t e s c o n t a i n i n g b o u n d m e t a l c a r b o n y l s

w e r e d r i e d u n d e r v a c u u m a t room t e m p e r a t u r e , d u e t o t h e t h e r m a l

r e a c t i v i t y o f t h e s e p o l y m e r s . T h e p o l y m e r s a r e s o l u b l e i n

c h l o r i n a t e d s o l v e n t s , t o l u e n e , b e n z e n e , e t h y l a c e t a t e , THF a n d

d i m e t h y l f o r m a m i d e b u t i n s o l u b l e i n d i e t h y l e t h e r , a l c o h o l s a n d

h y d r o c a r b o n s . The m e t a l a t e d p o l y m e r s show d e c r e a s e d s o l u b i l i t y

when c o m p a r e d w i t h t h e i r u n m e t a l l a t e d a n a l o g u e s . The m e t a l

c a r b o n y l c o n t a i n i n g p o l y m e r s w e r e t r e a t e d a s a i r a n d l i g h t

s e n s i t i v e , a n d s t a b i l i t i e s w e r e s i m i l a r t o t h o s e o f t h e i r

u n b o u n d m o n o m e r i c a n a l o g u e s . T a b l e s 5 . 7 - 5 . 1 2 show t h e w e i g h t s o f

t h e v a r i o u s c o m p o n e n t s u s e d i n t h e s y n t h e s e s o f t h e v a r i o u s

p o l y m e r s y s t e m s .

188

T a b l e 5 . 7 W e i g h t s ( g ) o f m a t e r i a l s u s e d i n t h e s y n t h e s i s o f n o n - m e t a l l a t e d c o p o l y m e r s ( 2 0 / 1 m o l e r a t i o ) .

Copolymer1 styrene MMA MA EA 4-vp 2-vp Vbipy

styrene-4-vp 5.0000 - - - 0.2524 - -styrene-2-vp 5.0000 - - - - 0.2524 -styrene-Vbipy 2.5000 - - - - - 0.2355MMA-4-vp - 5.0000 - - 0.2625 - -MMA-Vbipy - 2.0000 - - - - 0.1960MA-4-vp - - 5.0000 - 0.3053 - -EA-4-vp — - — 5 . 0 0 0 0 0 . 2 6 2 5 - -

*2% AIBN used in all preparations.

M e t a l c a r b o n y l c o m p l e x e s o f t h e s t y r e n e c o p o l y m e r s w e r e

p r e p a r e d b y r e a c t i o n w i t h p h o t o g e n e r a t e d [M(CO)g ( T H F ) ] .

M e t a l l a t e d c o p o l y m e r s o f t h e a c r y l a t e s a n d m e t h y l m e t h a c r y l a t e

w e r e n o t p r e p a r e d by t h i s r o u t e b e c a u s e o f t h e l i k e l i h o o d o f

b i n d i n g t o t h e o x y g e n s i t e s on t h e b a c k b o n e . The p o l y m e r s a m p l e s

w e r e d i s s o l v e d i n d r y THF a n d r e a c t e d w i t h a 1 : 1 m o l a r r a t i o o f

p y r i d i n e b i n d i n g s i t e s t o [M(CO) ( T H F ) ] . The THF was t h e n5

r e m o v e d by r o t a r y e v a p o r a t i o n a t 30°C. The p o l y m e r s w e r e t h e n

p r e c i p i t a t e d i n t o p e t r o l e u m e t h e r f r o m c h l o r o f o r m , f i l t e r e d on

s i n t e r e d g l a s s , w a s h e d w i t h e t h a n o l , a n d d r i e d u n d e r v a c u u m . I n

t h e c a s e o f t h o s e p o l y m e r p r e p a r e d f r o m t h e m e t a l c a r b o n y l

c o n t a i n i n g m o n o m e r s , t h e m o n o m e r s a n d i n i t i a t o r w e r e d i s s o l v e d ,

d e g a s s e d a n d h e a t e d u n d e r n i t r o g e n i n t h e m a n n e r d e s c r i b e d

e a r l i e r .

189

Table 5.8 Weights (g) of monomers and metal carbonyl containing comonomers used in the synthesis of some of the polymer- bound metal carbonyls (20/1 mole ratio).

P o l y m e r Monomer M(CO) ( 4 - v p )5

M(CO) ( 2 - v p ) M(CO) ( V b i p y )4

s t y r e n e - W(CO) ( 4 - v p )

5

2 . 0 0 0 0 0 . 4 1 2 0 - -

s t y r e n e -C r ( C O ) g ( 4 - v p ) 2 . 0 0 0 0 0 . 2 8 5 4 - -

s t y r e n e - Mo(CO) ( 4 - v p )

52 . 0 0 0 0 0 . 3 2 8 0 - -

s t y r e n e - W(CO) ( 2 - v p )

b

2 . 0 0 0 0 - 0 . 4 1 2 0 -

s t y r e n e - Cr (CO) ( 2 - v p )o

2 . 0 0 0 0 - 0 . 2 8 5 8 -

s t y r e n e - W(CO) ( V b i p y )

41 . 5 0 0 0 - - 0 . 3 5 4 4

s t y r e n e - Cr (CO) ( V B i p y )

41 . 5 0 0 0 - - 0 . 2 5 9 5

s t y r e n e -Mo(CO)4 ( V b i p y ) 1 . 5 0 0 0 - - 0 . 2 9 1 1

MMA- W(CO) ( 4 - v p )

b

2 . 5 0 0 0 0 . 5 3 6 0 - -

HMA- Cr (CO) ( 4 - v p )

b

2 . 5 0 0 0 0 . 3 7 1 0 - -

MMA- W(CO)4 ( V b i p y ) 1 . 5 0 0 0 - - 0 . 3 6 8 7

EA-W(CO) ( 4 - v p )

b

2 . 5 0 0 0 0 . 5 3 5 7 - -

EA-C r ( C O ) 5 ( 4 - v p ) 2 . 5 0 0 0 0 . 3 7 1 0 - -

EA-W(CO) ^ ( V b i p y ) 1 . 5 0 0 0 - - 0 . 3 6 8 7

MA-W(CO)s ( 4 - v p ) 2 . 5 0 0 0 0 . 6 2 3 0 - -

vp “ vlnylpyrldine, Vbipy ■ 4-vinyl-4'-methy-2,2’-bipyridyl MMA = methylmethacrylate, EA = Ethyl acrylate,NA e Hethyl acrylate. 2% AIBN used In all cases.

190

Table 5.8 Polymers of styrene and [W(CO)s(4-vp)] with free 4-vp.

R a t i o o f 4 - v p / s t y r e n e

s t y r e n e [W( CO) ^ ( 4 - v p ) ] 4 - v p AIBN

P [ 4 - v p - W(CO) ( 4 - v p ) ]

- 0 . 3 0 6 0 1 . 5 0 0 0 0 . 0 3 6 1

1 / 5 1 . 2 6 7 0 0 . 2 6 1 0 0 . 2 5 5 8 0 . 0 3 5 7

1 / 1 0 1 . 2 6 7 0 0 . 2 6 1 0 0 . 1 2 8 0 0 . 0 3 3 2

1 / 2 0 1 . 2 6 7 0 0 . 2 6 1 0 0 . 0 6 4 0 0 . 0 3 1 8

1 / 4 0 1 . 2 6 7 0 0 . 2 6 1 0 0 . 0 3 2 0 0 . 0 3 1 2

T a b l e 5 . 9 P o l y m e r s o f [W(CO) ( 4 - v p ) ] a n d s t y r e n e w i t h f r e e 2 - v p .5

R a t i o o f 2 - v p / s t y r e n e

s t y r e n e [W (CO ) ( 4 - v p ) ]b 2 - v p AIBN

1 / 1 0 . 6 0 6 8 0 . 1 2 5 0 0 . 6 1 2 5 0 . 0 3 0 5

1 / 5 1 . 2 1 3 6 0 . 2 5 0 0 0 . 2 4 2 5 0 . 0 3 1 7

1 / 1 0 1 . 2 1 3 6 0 . 2 5 0 0 0 . 1 2 2 5 0 . 0 3 4 11 / 2 0 1 . 2 1 3 6 0 . 2 5 0 0 0 . 0 6 1 3 0 . 0 2 6 9

191

T a b l e 5 . 1 0 P o l y m e r s o f [W(CO) ( 2 - v p ) ] a n d s t y r e n e ( 1 / 2 0 m o l e5

r a t i o ) f r e e 2 - v p .

R a t i o o f s t y r e n e [W(CO)5 ( 2 - v p ) ] 2 - v p AIBN

2 - v p / s t y r e n e

1 / 5 0 . 9 7 5 9 0 . 2 0 1 8 0 . 2 0 0 9 0 . 0 2 7 9

1 / 1 0 0 . 9 8 3 8 0 . 2 0 3 2 0 . 1 0 4 4 0 . 0 2 4 7

1 / 2 0 0 . 9 8 0 7 0 . 2 0 3 8 0 . 0 5 0 6 0 . 0 2 4 1

P [ ( 2 - v p - W(CO) ( 2 - v p ) ]b

- 0 . 1 9 9 6 1 . 0 0 0 4 0 . 0 2 5 0

All weights in grams.

T a b l e 5 . 1 1 P o l y m e r s o f [W(CO)4 ( 4 - v i n y l - 4 ' - m e t h y l - 2 , 2 ' - b i p y ) ]

( 1 / 2 0 m o l e r a t i o ) a n d s t y r e n e w i t h f r e e 4 - v p .

R a t i o o f

4 - v p / s t y r e n e

s t y r e n e [ W ( C O ) ^ ( V b i p y ) ] 4 - v p AIBN

1 / 5 0 1 . 2 0 0 0 0 . 2 8 3 5 0 . 0 2 4 2 0 . 0 3 0 2

1 / 3 0 1 . 2 0 0 0 0 . 2 8 3 5 0 . 0 4 0 4 0 . 0 3 0 51 / 2 0 1 . 2 0 0 0 0 . 2 8 3 5 0 . 0 6 0 6 0 . 0 3 0 9

1 / 1 0 1 . 2 0 0 0 0 . 2 8 3 5 0 . 1 2 1 2 0 . 0 3 2 1

All w e i g h t s in grams.

192

Table 5.12 Syntheses of copolymers of different metal loadings.

L o a d i n g s t y r e n e [W(CO) ( 4 - v p ) ]5

AIBN

1 : 1 0 0 0 5 . 0 0 0 0 0 . 0 2 0 6 0 . 1 0 0 4

1 : 5 0 0 5 . 0 0 0 0 0 . 0 4 1 2 0 . 1 0 0 8

1 : 2 0 0 3 . 0 0 0 0 0 . 0 6 1 8 0 . 0 6 1 2

1 : 1 0 0 3 . 0 0 0 0 0 . 1 2 3 6 0 . 0 6 2 0

1 : 4 0 3 . 0 0 0 0 0 . 3 0 8 9 0 . 0 6 6 2

1 : 3 0 3 . 0 0 0 0 0 . 4 1 2 0 0 . 0 6 8 2

1 : 1 0 1 . 5 0 0 0 0 . 6 0 6 8 0 . 0 4 2 3

1: 5 a 1 . 0 0 0 0 0 . 8 2 4 0 0 . 0 3 2 0

L o a d i n g s greater 1:5 rendered the p o l y m e r s insoluble.

5 . 4 . 1 P r e p a r a t i o n o f P o l y m e r - B o u n d D i p y r i d y l m e t h a n e .

A c o p o l y m e r o f s t y r e n e a n d 2 - v i n y l p y r i d i n e ( 2 0 / 1 m o l e

r a t i o ) was p r e p a r e d by f r e e r a d i c a l p o l y m e r i s a t i o n a s i n d i c a t e d

e a r l i e r i n s e c t i o n 5 . 4 . The l i t h i u m s a l t o f 2 - m e t h y l p y r i d i n e was

p r e p a r e d by t r e a t i n g 2 - m e t h y l p y r i d i n e ( 0 . 3 cm3 ) w i t h

n - b u t y l l i t h i u m ( M e r c k , 1 . 6 5 cm3 o f a 15 % s o l u t i o n i n h e x a n e ) a t

room t e m p e r a t u r e u n d e r a n i t r o g e n a t m o s p h e r e . A s o l u t i o n ( 0 . 7 5 g

i n 2 cm3 o f d r y t o l u e n e ) o f t h e p o l y m e r was t h e n a d d e d a n d t h e

r e s u l t i n g m i x t u r e was s t i r r e d f o r 8 h o u r s . F o l l o w i n g t h i s , i c e

( 1 0 cm ) was a d d e d c a r e f u l l y a n d t h e s o l u t i o n was e x t r a c t e d w i t h

d i c h l o r o m e t h a n e ( 4 0 cm ) . The o r g a n i c f r a c t i o n was t h e n

c o n c e n t r a t e d by r o t a r y e v a p o r a t i o n a n d t h e p o l y m e r was

p r e c i p i t a t e d by a d d i t i o n t o p e t r o l e u m e t h e r .

193

5.4.2 Anionic Copolymerisation of a-methylstyrene.

M e t h y l s t y r e n e was c o p o l y m e r i s e d w i t h 4 - v i n y l p y r i d i n e a n d

[M(CO) ( 4 - v p ) ] by a n a n i o n i c m e c h a n i s m , u s i n g s o d i u m n a p h t h a l i d e5

a s t h e c a t a l y s t a n d THF a s t h e s o l v e n t . S o d i u m n a p h t h a l i d e

r e a c t s r a p i d l y w i t h v i n y l g r o u p s p r o d u c i n g r a d i c a l i o n s w h i c h

q u i c k l y d i m e r i s e , d e s t r o y i n g t h e r a d i c a l a c t i v i t y a n d l e a v i n g a

d i a n i o n c a p a b l e o f g r o w t h a t b o t h e n d s . T h i s i n i t i a t i o n p r o c e s s

i s q u i t e r a p i d c o m p a r e d t o p r o p a g a t i o n , a n d h e n c e t h e g r o w t h o f

a l l t h e p o l y m e r c h a i n s i s s t a r t e d a l m o s t a t o n e t i m e 7 6a .

P o l y m e r s w i t h v e r y n a r r o w m o l e c u l a r d i s t r i b u t i o n s u s u a l l y

r e s u l t . B o t h t h e c a t a l y s t a n d t h e g r o w i n g c h a i n s a r e e a s i l y

d e s t r o y e d b y o x y g e n , w a t e r , c a r b o n d i o x i d e , a l c o h o l s , a n d many

o t h e r i m p u r i t i e s . I f t h e s e s u b s t a n c e s a r e r i g o r o u s l y e l i m i n a t e d ,

t h e c h a i n s a r e c a p a b l e o f f u r t h e r g r o w t h e v e n i f t h e s u p p l y o f

monomer i s d e p l e t e d ; t h e y c o n s t i t u t e a " l i v i n g " p o l y m e r s y s t e m ,

d e f i n e d a s o n e i n w h i c h t h e r e i s no t e r m i n a t i o n . P o l y m e r i s a t i o n

c a n c o n t i n u e when m o r e monomer o f t h e s am e t y p e o r d i f f e r e n t i s

a d d e d .

Materials

N a p h t h a l e n e (BDH) was s u b l i m e d u n d e r v a c u u m b e f o r e u s e .

So d i u m (BDH) was r e a g e n t g r a d e a n d was s t o r e d u n d e r p a r a f f i n

o i l . The o u t e r t a r n i s h e d c r u s t was r e m o v e d a n d t h e s o d i u m c u t

i n t o s m a l l p i e c e s a n d w a s h e d w i t h d r y THF b e f o r e u s e . THF a n d

4 - v i n y l p y r i d i n e w e r e p u r i f i e d a s a l r e a d y d e s c r i b e d .

a - M e t h y l s t y r e n e was w a s h e d w i t h 10% NaOH ( 3 X ) , d i s t i l l e d w a t e r

( 6 X ) , a n d d i s t i l l e d u n d e r v a c u u m . I t was t h e n d e g a s s e d w i t h a

194

s t r e a m o f a r g o n a n d s t o r e d o v e r c a l c i u m h y d r i d e a t 4°C u n t i l

r e q u i r e d . M e t h a n o l was r e a g e n t g r a d e a n d u s e d w i t h o u t f u r t h e r

p u r i f i c a t i o n .

P r e p a r a t i o n o f sodium n a p h t h a l i d e

A t wo n e c k e d r o u n d - b o t t o m e d f l a s k ( r b f ) was f i t t e d w i t h a

n i t r o g e n i n l e t , a r e f l u x c o n d e n s e r , a n d a C a C l 2 g u a r d t u b e . The

f l a s k was c h a r g e d w i t h n a p h t h a l e n e ( 1 . 5 g ) i n 50 cm3 o f d r y

d e g a s s e d THF a n d f r e s h l y c u t s o d i u m ( 1 . 5 g ) , a n d t h e s o l u t i o n

was s t i r r e d a t room t e m p e r a t u r e u n d e r a c o n t i n u o u s n i t r o g e n

p u r g e . A f t e r 10 m i n u t e s d a r k g r e e n s o d i u m n a p h t h a l i d e f o r m e d .

T he s o l u t i o n was s t i r r e d f o r a f u r t h e r 2 h o u r s .

P r o c e d u r e

A d r y 250 cm3 t h r e e - n e c k e d r b f was f i t t e d w i t h a r u b b e r

s e p t u m , g a s i n l e t , a n d a CaC^2 d r y i n g t u b e . The v e s s e l was

p u r g e d w i t h a r g o n f o r a b o u t 15 m i n u t e s . The monomers w e r e

d i s s o l v e d i n 50 cm3 o f THF a n d a d d e d t o t h e f l a s k . The s o l u t i o n

was c o o l e d t o - 8 0 ° C u s i n g a THF s l u r r y b a t h , a n d a l l o w e d t o

e q u i l i b r a t e f o r a b o u t 15 m i n u t e s . The f r e s h l y p r e p a r e d c a t a l y s t

was a d d e d v i a s y r i n g e . A d e e p r e d c o l o u r a p p e a r e d i m m e d i a t e l y a s

t h e s t y r e n e a n i o n s f o r m e d . A f t e r a f e w m i n u t e s , t h e c h a i n s w e r e

t e r m i n a t e d by i n j e c t i n g m e t h a n o l ( 4 cm ) . The r e d c o l o u r

d i s a p p e a r e d on a d d i t i o n o f t h e m e t h a n o l , a l i g h t g r e e n c o l o u r

p e r s i s t i n g . The f l a s k was warmed t o r oo m t e m p e r a t u r e a n d t h e

s o l u t i o n c o n c e n t r a t e d t o a b o u t 15 cm3 . The p o l y m e r was

p r e c i p i t a t e d i n p e t r o l e u m e t h e r a n d d r i e d u n d e r va cu um.

195

T a b l e 5 . 1 2 S y n t h e s e s o f a - m e t h y l s t y r e n e c o p o l y m e r s ( 2 0 / 1 m o l e

r a t i o ) .

a - m e t h y l s t y r e n e 4 - v p Cr (CO) ( 4 - v p )t> W(CO) ( 4 - v p )D

4 . 5 0 1 8 0 . 2 0 2 3 - -

2 . 0 3 7 0 - - 0 . 3 6 5 2

2 . 0 1 1 3 - 0 . 2 5 1 2 -

196

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